拟南芥AtLH基因过量表达引起叶向下性卷曲和晚开花

AtLH基因是BcpLH基因在拟南芥(Arapsis thaliana L.)中的同源基因,含有两个编码双链RNA结合蛋白的结构域.在大白菜叶球发育过程中,BcpLH基因与包叶的卷曲有关.为研究AtLH的基因对叶卷曲这一重要生物学现象的调控作用,构建了35S:AtLH基因的正义表达载体并转化拟南芥.与野生型比较页言,转基因植株的花和叶中AtLH的表达量有显著增加,成为AtLH基因过量的植株.这些植株的莲座叶向外或向下卷曲,呈现明显的偏上性生长;而且抽苔和开花时间延迟;在营养生长期其短缩茎的叶腑处着生数个侧茎,表现为顶端优势减弱;在生殖生长期二级花序减少使得主花序更加发达,表现为顶端优势增强,转基因植株对激素的敏感性改变,IAA剌激根生长的作用增强,ABA抑制根生长的作用减弱.由此可见,AtLH基因的过量表达可引起转基因植株的叶片向下卷曲.     

拟南芥AtLH基因过量表达引起叶向下性卷曲和晚开花(英文)

AtLH基因是BcpLH基因在拟南芥(Arabidopsis thealiana L.)中的同源基因,含有两个编码双链RNA结合蛋白的结构域。在大白菜叶球发育过程中,BcpLH基因与包叶的卷曲有关。为研究AtLH基因对叶卷曲这一重要生物学现象的调控作用,构建了35S:AtLH基因的正义表达载体并转化拟南芥。与野生型比较而言,转基因植株的花和叶中AtLH的表达量有显著增加,成为AtLH基因过量表达的植株。这些植株的莲座叶向外或向下卷曲,呈现明显的偏上性生长;而且抽苔和开花时间延迟;在营养生长期其短缩茎的叶腋处着生数个侧茎,表现为顶端优势减弱;在生殖生长期二级花序减少使得主花序更加发达,表现为顶端优势增强;转基因植株对激素的敏感性改变,IAA刺激根生长的作用增强,ABA抑制根生长的作用减弱。由此可见,AtLH基因的过量表达可引起转基因植株的叶片向下卷曲。     

The role of EMF1 in regulating the vegetative and reproductive transition in Arabidopsis thaliana (Brassicaceae)

To understand the genetic regulation of vegetative to reproductive transition in higher plants, further characterization of the Arabidopsis mutant embryonic flower1, emf1, was conducted. Using three flowering symptoms, we showed that emf1 mutants could only grow reproductive and not rosette shoots under five different growth conditions. The mutant embryos did not produce the typical tunica–corpus shoot apical structures at the heart-, torpedo-, and mature stages. The divergent shoot apical development during mutant and wild-type embryogenesis indicated that the wild-type EMF1 gene was expressed in early embryogenesis. Mutations in the EMF1 gene affected the embryonic shoot apical development and caused the germinating embryo and regenerating callus to grow inflorescence, instead of rosette, shoots. Our results support the hypothesis that the EMF1 gene regulates the switch between vegetative and reproductive growth in Arabidopsis.     

The Arabidopsis compact inflorescence genes: phase-specific growth regulation and the determination of inflorescence architecture

During their life cycle, higher plants pass through a series of growth phases that are characterized by the production of morphologically distinct vegetative and reproductive organs and by different growth patterns. Three major phases have been described in Arabidopsis: juvenile vegetative, adult vegetative, and reproductive. In this report we describe a novel, phase-specific mutant in Arabidopsis, compact inflorescence (cif). The most apparent aspect of the cif phenotype is a strong reduction in the elongation of internodes in the inflorescence, resulting in the formation of a floral cluster at the apical end of all reproductive shoots. Elongation and expansion of adult vegetative rosette leaves are also compromised in mutant plants. The onset of the cif trait correlates closely with morphological changes marking the phase transition from juvenile to adult, and mutant plants produce normal flowers and are fully fertile. Hence the cif phenotype appears to be adult vegetative phase-specific. Histological sections of mutant inflorescence internodes indicate normal tissue specification, but reduced cell elongation compared to wild-type. compact inflorescence is inherited as a two-gene trait involving the action of a recessive and a dominant locus. These two cif genes appear to be key components of a growth regulatory pathway that is closely linked to phase change, and specifies critical aspects of plant growth and architecture including inflorescence internode length.     

Growth and reproduction of Arabidopsis thaliana in relation to storage of starch and nitrate in the wild-type and in starch-deficient and nitrate-uptake-deficient mutants

We have investigated the interactions between resource assimilation and storage in rosette leaves, and their impact on the growth and reproduction of the annual species Arabidopsis thaliana. The resource balance was experimentally perturbed by changing (i) the external nutrition, by varying the nitrogen supply; (ii) the assimilation and reallocation of resources from rosette leaves to reproductive organs, by cutting or covering rosette leaves at the time of early flower bud formation, and (iii) the internal carbon and nitrogen balance of the plants, by using isogenic mutants either lacking starch formation (PGM mutant) or with reduced nitrate uptake (NU mutant). When plants were grown on high nitrogen, they had higher concentrations of carbohydrates and nitrate in their leaves during the rosette phase than during flowering. However, these storage pools did not significantly contribute to the bulk flow of resources to seeds. The pool size of stored resources in rosette leaves at the onset of seed filling was very low compared to the total amount of carbon and nitrogen needed for seed formation. Instead, the rosette leaves had an important function in the continued assimilation of resources during seed ripening, as shown by the low seed yield of plants whose leaves were covered or cut off. When a key resource became limiting, such as nitrogen in the NU mutants and in plants grown on a low nitrogen supply, stored resources in the rosette leaves (e.g. nitrogen) were remobilized, and made a larger contribution to seed biomass. A change in nutrition resulted in a complete reversal of the plant response: plants shifted from high to low nutrition exhibited a seed yield similar to that of plants grown continuously on a low nitrogen supply, and vice versa. This demonstrates that resource assimilation during the reproductive phase determines seed production. The PGM mutant had a reduced growth rate and a smaller biomass during the rosette phase as a result of changes in respiration caused by a high turnover of soluble sugars ( Caspar et al. 1986 ; W. Schulze et al. 1991 ). During flowering, however, the vegetative growth rate in the PGM mutant increased, and exceeded that of the wild-type. By the end of the flowering stage, the biomass of the PGM mutant did not differ from that of the wild-type. However, in contrast to the wild-type, the PGM mutant maintained a high vegetative growth rate during seed formation, but had a low rate of seed production. These differences in allocation in the PGM mutant result in a significantly lower seed yield in the starchless mutants. This indicates that starch formation is not only an important factor during growth in the rosette phase, but is also important for whole plant allocation during seed formation. The NU mutant resembled the wild-type grown on a low nitrogen supply, except that it unexpectedly showed symptoms of carbohydrate shortage as well as nitrogen deficiency. In all genotypes and treatments, there was a striking correlation between the concentrations of nitrate and organic nitrogen and shoot growth on the one hand, and sucrose concentration and root growth on the other. In addition, nitrate reductase activity (NRA) was correlated with the total carbohydrate concentration: low carbohydrate levels in starchless mutants led to low NRA even at high nitrate supply. Thus the concentrations of stored carbohydrates and nitrate are directly or indirectly involved in regulating allocation.     

Revisiting phase transition during flowering in Arabidopsis

Single-phase transition during flowering has been suggested by Hempel and Feldman (1994) [Planta 192: 276]. When early flowering ecotypes of Arabidopsis were microscopically observed, a long day signal simultaneously induced the acropetal (bottom to top) production of flower primordia and the basipetal (top to bottom) differentiation of paraclades (axillary flowering shoots) from the axils of pre-existing leaf primordia. However, this model could not account for the production of an extra number of secondary shoots in the TERMINAL FLOWER 1 overexpressor line or AGL20 overexpressor line in Columbia background with a functional allele of FRIGIDA. We report here that Columbia with a functional allele of FRIGIDA under long days and Columbia under short days show an inflorescence-producing phase between the vegetative and the flower-producing phases, supporting two-step phase transition during flowering. In addition, a late-flowering mutant, fwa shows an inflorescence phase but fca, fy and fve follow a single-phase transition, suggesting flowering time mutations have different effects on phase transition during flowering.     

Developmental disaster1: A novel mutation causing defects during vegetative and inflorescence development in maize (Zea mays, Poaceae)

Axillary meristems, which give rise to branches and flowers, play a critical role in plant architecture and reproduction. To understand how axillary meristems initiate, we have screened for mutants with defects in axillary meristem initiation to uncover the genes controlling this process. These mutants, called the barren class of mutants in maize (Zea mays), have defects in axillary meristem initiation during both vegetative and reproductive development. Here, we identify and characterize a new member of the barren class of mutants named Developmental disaster1 (Dvd1), due to the pleiotropic effects of the mutation. Similar to the barren mutants, Dvd1 mutants have fewer branches, spikelets, florets, and floral organs in the inflorescence due to defects in the initiation of axillary meristems. Furthermore, double mutant analysis with teosinte branched1 shows that dvd1 also functions in axillary meristems during vegetative development. However, unlike the barren mutants, Dvd1 mutants are semidwarf due to the production of shorter internodes, and they produce leaves in the inflorescence due to the outgrowth of bract leaf primordia. The suite of defects seen in Dvd1 mutants, together with the genetic interaction of Dvd1 with barren inflorescence2, suggests that dvd1 is a novel regulator of axillary meristem and internode development.     

The Export and Distribution of 14C-labelled Assimilates from each Leaf on the Shoot of Lolium temulentum during Reproductive and Vegetative Growth

In both reproductive and vegetative plants of Lolium temulentumL., the export of ¹⁴C-labelled assimilates from each healthyleaf on the main shoot to terminal meristem, stem, tillers,and roots was measured each time a new leaf was expanded, fora period of 5 to 6 weeks. Some labelled assimilates moved fromeach leaf on the main shoot to every meristem in the same shoot,as well as to the tops and roots of adjacent organically attachedtillers. The terminal meristem of the reproductive shoot, which includedthe developing inflorescence, received 70–80 per centof the carbon assimilated by the emerged portion of the growingleaf, 15–25 per cent of the carbon assimilated by thetwo youngest expanded leaves, and 5–10 per cent of thatfrom each of the older leaves. A similar pattern of carbon supplyto the terminal meristem was found in vegetative shoots, exceptthat older leaves on young vegetative shoots supplied even lessof their carbon to the terminal meristem. The general conclusionis that developing leaves at the tip of the shoot receive aboutthe same proportion of carbon from each leaf as does a developinginflorescence. Young expanded leaves provided most labelled assimilates forstem growth; during both reproductive and vegetative growth,expanded leaves increased their export of labelled carbon tostem, and exported less of their ¹⁴C to roots and sometimesto tillers. In these reproductive and vegetative shoots, grown in a constantexternal environment, the major changes in the pattern of distributionof labelled assimilates appeared to be the result of increasedmeristematic activity in stem internodes; the development ofan inflorescence had no obvious direct effect on the carboneconomy of shoots.     

Bi-directional inflorescence development inArabidopsis thaliana: Acropetal initiation of flowers and basipetal initiation of paraclades

In this study we investigated Arabidopsis thaliana (L.) Heynh. inflorescence development by characterizing morphological changes at the shoot apex during the transition to flowering. Sixteen-hour photoperiods were used to synchronously induce flowering in vegetative plants grown for 30 d in non-inductive 8-h photoperiods. During the first inductive cycle, the shoot apical meristem ceased producing leaf primordia and began to produce flower primordia. The differentiation of paraclades (axillary flowering shoots), however, did not occur until after the initiation of multiple flower primordia from the shoot apical meristem. Paraclades were produced by the basipetal activation of buds from the axils of leaf primordia which had been initiated prior to photoperiodic induction. Concurrent with the activation of paraclades was the partial suppression of paraclade-associated leaf primordia, which became bract leaves. The suppression of bract-leaf primordia and the abrupt initiation of flower primordia during the first inductive photoperiod is indicative of a single phase change during the transition to flowering in photoperiodically induced Arabidopsis. Morphogenetic changes characteristic of the transition to flowering in plants grown continuously in 16-h photoperiods were qualitatively equivalent to the changes observed in plants which were photoperiodically induced after 30 d. These results suggest that Arabidopsis has only two phases of development, a vegetative phase and a reproductive phase; and that the production of flower primordia, the differentiation of paraclades from the axils of pre-existing leaf primordia and the elongation of internodes all occur during the reproductive phase.     

Overexpression of EVE1, a novel ubiquitin family protein, arrests inflorescence stem development in Arabidopsis

In Arabidopsis, inflorescence stem formation is a critical process in phase transition from the vegetative to the reproductive state. Although inflorescence stem development has been reported to depend on the expression of a variety of genes during floral induction and repression, little is known about the molecular mechanisms involved in the control of inflorescence stem formation. By activation T-DNA tagging mutagenesis of Arabidopsis, a dominant gain-of-function mutation, eve1-D (eternally vegetative phase1-Dominant), which has lost the ability to form an inflorescence stem, was isolated. The eve1-D mutation exhibited a dome-shaped primary shoot apical meristem (SAM) in the early vegetative stage, similar to that seen in the wild-type SAM. However, the SAM in the eve1-D mutation failed to transition into an inflorescence meristem (IM) and eventually reached senescence without ever leaving the vegetative phase. The eve1-D mutation also displayed pleiotropic phenotypes, including lobed and wavy rosette leaves, short petioles, and an increased number of rosette leaves. Genetic analysis indicated that the genomic location of the EVE1 gene in Arabidopsis thaliana corresponded to a bacterial artificial chromosome (BAC) F4C21 from chromosome IV at ～17cM which encoded a novel ubiquitin family protein (At4g03350), consisting of a single exon. The EVE1 protein is composed of 263 amino acids, contains a 52 amino acid ubiquitin domain, and has no glycine residue related to ubiquitin activity at the C-terminus. The eve1-D mutation provides a way to study the regulatory mechanisms that control phase transition from the vegetative to the reproductive state.     

<Emphasis Type="Italic">SINGLE FLOWER TRUSS</Emphasis> regulates the transition and maintenance of flowering in tomato

The characterisation of the single flower truss ( sft) mutant phenotype of tomato ( Lycopersicon esculentum Mill.), as well as its genetic interactions with other mutations affecting FALSIFLORA ( FA) and SELF PRUNING ( SP) genes, has revealed that SFT is a key gene in the control of floral transition and floral meristem identity. The single sft mutation produces a late-flowering phenotype in both long-day and short-day conditions. In combination with fa, a mutation affecting the tomato gene orthologous to LFY, sft completely blocks the transition to flowering in this species. Thus, the phenotype of the sft fa double mutants indicates that SFT and FA participate in two parallel pathways that regulate the switch from vegetative to reproductive phase in tomato, and that both genes are indispensable for flowering. On the other hand, the replacement of flowers by vegetative shoots observed in the sft inflorescence suggests that SFT regulates flower meristem identity during inflorescence development of tomato. In addition to these two main functions, SFT is involved in the development of both flowers and sympodial shoots of tomato. First, the mutation produces a partial conversion of sepals into leaves in the first floral whorl, and a reduction in the number of floral organs, particularly carpels. Secondly, the sympodial development in the mutant plants is altered, which can be related to the interaction between SFT and SP, a gene controlling the number of nodes in sympodial shoots. In fact, we have found that the sft phenotype is epistatic to that of sp, and that the level of SP mRNA in the apical buds of sft around flowering is reduced. SFT can therefore co-ordinate the regulation of two simultaneous developmental processes in the tomato apical shoot, the promotion of flowering in one sympodial segment and the vegetative development of the next segment.     

Architecture of the pruned tree: impact of contrasted pruning procedures over 2 years on shoot demography and spatial distribution of leaf area in apple (Malus domestica)

BACKGROUND AND AIMS: Demography and spatial distribution of shoots are rarely studied on pruned trees. The present 2-year study deals with the effect of pruning strategies on shoot demography and development, and consequences on the spatial distribution of leaf area in three architecturally contrasted - from type II to IV - apple cultivars: 'Scarletspur Delicious', 'Golden Delicious' and 'Granny Smith'. METHODS: All trees were initially subjected during 5 years to Central Leader training with winter heading on all long shoots. For 2 years, half of the trees were further trained with Centrifugal training, where removal of flowering shoots - called extinction pruning - was carried out along the trunk and at the bottom of branches at flowering time. During these 2 years, shoot type (vegetative, inflorescence) and length, and the three-dimensional spatial distribution of all shoots were assessed with an electromagnetic digitizer. KEY RESULTS: Shoot demography, frequency of transitions toward an inflorescence from either an inflorescence (bourse-over-bourse) or a vegetative shoot (trend toward flowering), and the number of bourse-shoots per bourse were strongly affected by cultivar, with little influence of tree manipulation. In contrast, the proportion of vegetative long shoots developing from previous year latent buds was significantly lower in Centrifugal-trained trees for the three cultivars. Canopy volume showed large variations between cultivars, but only that of 'Granny Smith' was affected by tree manipulation in the 2 years. Spatial distribution of shoots varied significantly according to cultivar and manipulation. In 'Scarletspur Delicious' and, to a lesser extent 'Golden Delicious', the distribution of vegetative and flowering shoots in the outer and the inner parts, respectively, was not affected by tree manipulation. In contrast, in 'Granny Smith', vegetative shoots were stimulated in the periphery of Central Leader trees, whereas flowering shoots were stimulated in the periphery of Centrifugal-trained trees. CONCLUSIONS: In apple, the variability of responses to contrasted pruning strategies partly depends on the genetically determined growth and flowering habit of the cultivar.     

CaJOINTLESS is a MADS-box gene involved in suppression of vegetative growth in all shoot meristems in pepper

In aiming to decipher the genetic control of shoot architecture in pepper (Capsicum spp.), the allelic late-flowering mutants E-252 and E-2537 were identified. These mutants exhibit multiple pleiotropic effects on the organization of the sympodial shoot. Genetic mapping and sequence analysis indicated that the mutants are disrupted at CaJOINTLESS, the orthologue of the MADS-box genes JOINTLESS and SVP in tomato and Arabidopsis, respectively. Late flowering of the primary and sympodial shoots of Cajointless indicates that the gene functions as a suppressor of vegetative growth in all shoot meristems. While CaJOINTLESS and JOINTLESS have partially conserved functions, the effect on flowering time and on sympodial development in pepper, as well as the epistasis over FASCICULATE, the homologue of the major determinant of sympodial development SELF-PRUNING, is stronger than in tomato. Furthermore, the solitary terminal flower of pepper is converted into a structure composed of flowers and leaves in the mutant lines. This conversion supports the hypothesis that the solitary flowers of pepper have a cryptic inflorescence identity that is suppressed by CaJOINTLESS. Formation of solitary flowers in wild-type pepper is suggested to result from precocious maturation of the inflorescence meristem.     

Determination for inflorescence development is a stable state,separable from determination for flower development in Pisum sativum L. buds

Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.     

Branching pattern and inflorescence bud displacement in Flickingeria (Orchidaceae)

The vegetative architecture of Flickingeria is modular, consisting of three kinds of shoots of determinate growth. Species differ with respect to extent of branching and length of shoots, but branching is normally restricted to a few particular buds, the potential of which depends on their position.
All inflorescences are axillary, although some appear to be terminal. Inflorescences subtended by foliage leaves are displaced into a cavity in the stem, emerging on the abaxial side of the leaf base. The peripheral layers of the stem covering the inflorescence bud may be conspicuously extended and dry up so as to resemble a bract. The arrangement of the inflorescences is a distinctive specific character within the genus. A hypothesis for the evolution of character states is established. The growth and flowering strategy is discussed.     

Diversity of flowering and fruiting phenology of trees in a tropical deciduous forest in India

BACKGROUND AND AIMS: In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species. METHODS: Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles. KEY RESULTS: Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3-4 months) in dry-season and winter-flowering species, 6-9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized. CONCLUSIONS: The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.     

Keep on growing under drought: genetic and developmental bases of the response of rosette area using a recombinant inbred line population

Variation in leaf development caused by water deficit was analysed in 120 recombinant inbred lines derived from two Arabidopsis thaliana accessions, Ler and An‐1. Main effect quantitative trait loci (QTLs) and QTLs in epistatic interactions were mapped for the responses of rosette area, leaf number and leaf 6 area to water deficit. An epistatic interaction between two QTLs affected the response of whole rosette area and individual leaf area but only with effects in well‐watered condition. A second epistatic interaction between two QTLs controlled the response of rosette area and leaf number with specific effects in the water deficit condition. These effects were validated by generating and phenotyping new appropriate lines. Accordingly, a low reduction of rosette area was observed for lines with a specific allelic combination at the two interacting QTLs. This low reduction was accompanied by an increase in leaf number with a lengthening of the vegetative phase and a low reduction in individual leaf area with low reductions in epidermal cell area and number. Statistical analyses suggested that responses of epidermal cell area and number to water deficit in individual leaves were partly caused by delay in flowering time and reduction in leaf emergence rate, respectively.     

A morphological study of the development of the second inflorescences in strawberry (Fragaria×ananassa Duch.)

To clarify the timing of the differentiation of the first and second inflorescences in strawberry (Fragaria × ananassa Duch.), morphological changes on shoot apices during short day and low night temperature treatments were observed by scanning electron microscopy (SEM) and optical microscopy. Axillary buds just below the first inflorescence (axillary bud 1) became visible when sepal primordia of the primary flower were differentiated. By this time, other axillary buds had already developed. Axillary bud 1 developed four leaf primordia, and then a differentiated inflorescence at its summit. The phase transition of shoot apices from the vegetative to the reproductive phase may therefore trigger the differentiation of axillary bud 1 which is destined to develop into extension crowns.     

The SERRATE locus controls the formation of the early juvenile leaves and phase length in Arabidopsis

The development of the shoot can be divided into a series of distinct developmental phases based on leaf character-istics and inflorescence architecture. The relationship between phase length, defined by the number of organs produced, and the timing of the floral induction (V3-I1 transition) is relatively ill defined. Characterization of the serrate mutant (CS3257; Arabidopsis Biological Research Center) revealed defects in both vegetative and inflores-cence phase lengths, the timing of phase transitions, leaf number, the leaf initiation rate, and phyllotaxy. The timing of floral induction, however, is the same as in wild-type in extended short days as well as in short days, whereas the flowering time response to photoperiod is unaffected. SERRATE is shown to be required for the development of early juvenile leaves (V1) and to promote late juvenile leaf development (V2), while suppressing adult leaf (V3) and inflorescence development (I1 and I2). The se mutation supports the hypothesis that the timing of floral induction is independent of vegetative and inflorescence phase lengths. The role of SERRATE in the regulation of phase length and leaf identity is discussed.     

Consequences of the Elimination of Old Leaves upon Spring Phenological Events and the New Leaves Nutrient Concentration in a Wintergreen Woody Species in the Southern Hemisphere

Previous studies analyzed the importance of old leaves conservancy for wintergreen species plant growth only after early spring old leaves elimination. However, carbon and nutrient resources for growth could have already been translocated from old leaves to shoots during autumn. In this work, the effect of old leaves absence on the leaf mass per area (LMA, g m⁻²) and nutrient concentration of new spring leaves, shoot growth, and flowering was studied in Aristotelia chilensis, an Andean Patagonic woody wintergreen species of Argentina. Plants were studied after autumn defoliation (AD) or late winter defoliation (WD) and results were compared to those of undamaged control plants (CO). The new leaves LMA and mineral nutrient (N, P, K, and Mg) concentration values did not decrease in AD or WD compared to CO plants. Conversely, CO plants showed higher flowering intensity and shoot lengthening compared to AD or WD plants. There were not remarkable differences regarding the defoliation time, though non-flowering shoots grew in a lesser degree than the flowering shoots in WD plants. It was concluded that A. chilensis old leaves cohort is an important source to shoot growth and flowering but their absence does not affect the new leaves structure or nutritional status from early spring in either AD or in WD plants. New leaves formation probably is guaranteed by resources (carbon and nutrients) previously stored in stems or even in the buds containing the preformed leaves since March, by the end of summer. Provided the availability of complete resources for the new leaf flush independently of the old leaves A. chilensis would restore the carbon balance as soon as possible to resume the growth of heterotrophic tissues at normal rates. Endogenous response to counterbalance the old leaves absence on non-flowering shoots was more effective when there was greater lag time between defoliation and shoot growth resume. Flowering and non-flowering shoots compete for the available resources when A. chilensis have not yet expanded leaves and shoots supporting reproductive structures were stronger sinks compared to non-flowering shoots in WD plants.