Jasmonates Inhibit Flowering in Short-Day Plant Pharbitis nil

The role of jasmonates in the photoperiodic flower induction of short-day plant Pharbitis nil was investigated. The plants were grown in a special cycle: 72 h of darkness, 24 h of white light with lowered intensity, 24-h long inductive night, 14 days of continuous light. At 4 h of inductive night the cotyledons of non-induced plants contained about two times the amount of endogenous jasmonates (JA/JA-Me) compared to those induced. A 15-min long pulse of far red light (FR) applied at the end of a 24-h long white light phase inhibited flowering of P. nil. The concentration of jasmonates at 2 and 4 h of inductive night in the cotyledons of the plants treated with FR was similar. Red light (R) could reverse the effect of FR. R light applied after FR light decreased the content of jasmonates by about 50%. Methyl jasmonate (JA-Me) applied to cotyledons, shoot apices and cotyledon petioles of P. nil inhibited the formation of flower buds during the first half of a 24-h long inductive or 14-h long subinductive night. Application of JA-Me to the cotyledons was the most effective. None of the plants treated with JA-Me on the cotyledons in the middle of the inductive night formed terminal flower buds. The aspirin, ibuprofen and phenidone, jasmonates biosynthesis inhibitors partially reversed the effect of FR, stimulating the formation of axillary and terminal flower buds. Thus, the results obtained suggests that phytochrome system control both the photoperiodic flower induction and jasmonates metabolism. Jasmonates inhibit flowering in P. nil.     

Distribution of diamine oxidase activity and polyamine pattern in bean and soybean seedlings at different stages of germination

Diamine oxidase (DAO, EC 1.4.3.6.) activity and polyamine content were measured in the shoot apex, leaves, epicotyl, cotyledons, hypocotyl and roots of light-grown bean ( Phaseolus vulgaris L. cv. Lingot) and soybean ( Glycine max L. cv. Sakai) seedlings at 3 different stages of germination (5, 8 and 14 days) as well as in embryos and cotyledons from soaked seeds. No DAO activity was detected in embryos and cotyledons of either plants. In bean seedlings DAO activity was only detectable in the shoot apex, primary leaves and cotyledons, while in soybean the activity was only detectable in the hypocotyl and roots. During seedling growth, in both plants, a different pattern of DAO activity was observed. In both species spermidine and spermine were the most abundant polyamines in embryos and cotyledons. Cadaverine, absent in bean, was only detected in soybean embryos. In the seedlings of both plants, increasing gradients of putrescine, spermidine and spermine from base to shoot apex were found. A high concentration of cadaverine was present in soybean hypocotyls and roots. A possible correlation between DAO activity and the endogenous content of the preferential substrate is discussed in relation to the possible involvement of the enzyme in regulating the cellular level of polyamines.     

STUDIES ON THE SOLUBLE CARBOHYDRATES AND CARBOHYDRATE PRECURSORS IN GERMINATING SOYBEAN SEED

The total soluble carbohydrate fraction of the cotyledons and embryo axis of germinating soybean seedlings declined rapidly during the first 3 days of germination. This depletion began earlier in the embryo axis than in the cotyledon. The total carbohydrate content of the cotyledons of plants grown in light and plants grown in dark was approximately the same for the first 7 days of germination. Between day 9 and 13 the total carbohydrate content of the cotyledons of soybean seedlings grown in dark was higher than that of plants grown in light. The reducing sugar content of light-grown soybean cotyledons increased approximately 5-fold during the first 9 days of germination, whereas that of dark-grown soybean cotyledons increased more slowly during this interval. Reducing sugars in the embryo increased during the early stages of germination until they approximately equalled the total carbohydrate. Between day 4 and 13, oil was depleted more rapidly in the cotyledons of seedlings grown in light than those grown in the dark. The reserve carbohydrates of soybean embryos and cotyledons consisted primarily of low molecular weight oligosaccharides, particularly sucrose, stachyose, and raffinose. These compounds decreased rapidly during germination. The isocitritase activity in the cotyledons of germinating soybean seeds increased rapidly for the first 6 days of germination and then decreased for the next 7 days. The isocitritase activity of plants grown in the dark was higher than that of the plants grown in light at all stages of development, particularly between day 7 and 11.     

Apical Growth and Modification of the Development of Primordia During Re-flowering of Reverted Plants of Impatiens balsamina L

Impatiens balsamina L. was induced to flower by exposure to5 short days and then made to revert to vegetative growth byreturn to long days. After 9 long days reverted plants wereinduced to re-flower by returning them to short days. Petalinitiation began immediately and seven primordia already presentdeveloped into petals instead of into predominantly leaf-likeorgans. However, the arrangement of primordia at the shoot apex,their rate of initiation and size at initiation remained unchangedfrom the reverted apex, as did apical growth rate and the lengthof stem frusta at initiation. The more rapid flowering of thereverted plants than of plants when first induced, and the lackof change in apical growth pattern, imply that the revertedapices remain partially evoked, and that the apical growth patternand phyllotaxis typical of the flower, and already present inthe reverted plants, facilitate the transition to flower formation. Impatiens balsamina, flower reversion, partial evocation, shoot meristem, determination, leaf development     

Hormone-mediated regulative action of the sunflower shoot apex on growth and cation level in the cotyledons: an additional manifestation of apical control

Decapitation of the shoot apex of seedlings of Helianthus annuus Lin. above the cotyledonary node brought about promotion of growth in the cotyledons. Potassium level in the cotyledons of decapitated plants was higher, and that of sodium lower, than in those of intact plants. IAA applied to the cut stem surface imitated the effects of the apex. Application of kinetin to the cotyledons antagonized the apex or the auxin in their influence on growth and cation level. Labeled IAA applied to the cut stem surface penetrated into the cotyledons in significant amounts. It was concluded that growth and monovalent cation level in the cotyledons are regulated by auxin released from the shoot apex and that at least part of the auxin effect is exerted directly in the cotyledons. A function of the apex as a sink for cytokinins may also be involved in the control mechanism.     

Relation between the diameter of the growing shoot and the mature size of leaves and flower head of sunflower

Helianthus annuus L. cv. INRA 6501 plants were cultivated at irradiances of 15, 30 and 60 W m⁻² (400–700 nm) at 20°C and a relative humidity of 60% on a gravel culture subirrigated with Hoagland's nutrient solution. From 10 days after the opening of the cotyledons the diameter of the growing shoot increased linearly with time at a rate dependent on the irradiance. These measurements were continued until the flower bud became visible. By extrapolation of this linear growth to the day of anthesis the diameter of the stem below the flower head was predicted. This stem diameter had a constant ratio (9.7) to the measured diameter of the flower head. In the early stages of development of the plant it is proposed that the diameter of the growing shoot, supported by its vascular system, is a determinant of the size of the mature leaves. Later in the development the diameter of the growing shoot is a determinant of the diameter of the flower head. This change of function is caused by localised activity of the cambial cells which results in tangential growth in the vascular cylinder and ultimately in a hollow stem.     

Dynamics of IAA and cytokinins in flower tissues of transgenic tobacco mutant plants with mutant phenotype

A comparative analysis of IAA and total cytokinin contents at various developmental stages of floral morphogenesis (I–XII) in transgenic tobacco (Nicotiana tabacum L.) plants with mutant phenotypes was performed. Disturbances in flower structure were correlated with changes in the content and dynamics of these phytohormones. In plants with the phenotype “wavy corolla”, IAA content increased by three times as compared with control at stage VIII; in plants with the phenotype “longostyly”, IAA content increased gradually from VIII to XII stage and sharply (by nine times) at stage XII. In plants with the phenotype “wavy corolla”, total content of cytokinins was lower than in control at all developmental stages (except for stage I), whereas their dynamics coincided with that in control flowers. In plants with the phenotype “longostyly”, cytokinin content was twice lower than in control at early developmental stages, whereas it oscillated at later stages, approaching to control value at stage XII. It is supposed that differences observed could result from T-DNA insertion into plant own genes, which led to changes in the content and dynamics of phytohormones in developing flowers and production of anomalies in the flower structure.     

Physiological significance of indoleacetic acid and factors determining its level in cotyledons of Lupinus albus during germination and growth

The results demonstrate the profile of the endogenous indole-3-acetic acid (IAA) in the cotyledons of Lupinus albus L. ( L. termis Forssk.) during germination and seedling growth. The auxin level increases markedly after seed hydration, especially during the time of radicle emergence 24 h after the onset of imbibition. This rise is accompanied by a minimal IAA-oxidase activity, formation of indoleacetylaspartic acid (IAAsp) and an increase in the endogenous tryptophan and tryptophan-carboxyl-¹⁴C degradation, though the latter cannot account for the high IAA level detected during early stages of germination. It is believed that cotyledons are a source of IAA to the developing embryonic axis. – The auxin level drops in the cotyledons during seedling growth, 2–18 days after sowing. This is true also for IAAsp and tryptophan-degrading activity of enzyme extracts. Conversely, endogenous tryptophan is increasingly liberated up to day 14, and IAA-oxidase activity climbs to a peak detected on day 12, prior to the appearance of senescence in the cotyledons. – The physiological significance of IAA and the factors regulating its level in the cotyledons during germination and growth are discussed.     

A HISTOCHEMICAL STUDY OF THE SEEDLING SHOOT APICAL MERISTEM OF PINUS LAMBERTIANA

Vernalized seeds of Pinus lambertiana were scarified and planted in perlite. At 5, 8, 10, 13 and 16 days after planting, seedlings were selected for morphological examination and histochemical study. The shoot apical meristem consisted of a relatively homogeneous population of cells at 5 days. Cytohistological zonation was observed in the meristem by the eighth day and needle primordia initiation began at this time. Acid phosphatase (AP) activity was high in the extreme tip of the apex at 5 days. At 8 days AP activity was intense in the peripheral zone but weak in the apical initial and central mother cell zones. The apical meristem of the 10–16-day-old seedlings exhibited high AP activity in the peripheral zone only during the early stages of needle primordia initiation. The distribution of cytoplasmic and nuclear protein-bound SH was correlated with cytohistological zonation. Protein-bound SH was distributed relatively uniformly at 5 days, but by the eighth day the 4 cytohistological zones contained differential quantities. Succinic dehydrogenase (SD) activity was observed throughout the apex at 5 days, but by the eighth day the apical initial and central mother cell zones exhibited differentially greater levels of SD activity. Irradiation with 500 R of X-rays at 7 days after planting completely inhibited needle primordia initiation and disrupted the cytohistological zonation of the apex. Correlated with the inhibition of needle primordia initiation was the loss of SD activity in the apical initial and central mother cell zones. Irradiation also resulted in the gradual loss of protein-bound SH from the cytoplasm of the apical initial, central mother cell and peripheral zone.     

Effect of Crinipellis perniciosa Infection on Abscission of Cacao Cotyledons, Reserve Mobilization and Dry Matter Partitioning

Infection by Crinipellis perniciosa on cacao seedlings prevented the abscission of cotyledons which normally abscise within 32–61 days from seed sowing. The early growth and development of control and artificially inoculated seedlings was investigated for root dry mass (RDM), shoot dry mass (SDM), shoot‐to‐root ratio (SRR), total dry mass (TDM), cotyledonary dry mass (CDM) and cotyledonary water content (CWC). Cotyledonary reserve mobilization was estimated at 69 and 56% at 5 weeks and 79 and 64% at 8 weeks in control and infected seedlings, respectively. Infection induced the enlargement of tissues but was not accompanied by an increase in dry mass. Infection both delayed and reduced the utilization of cotyledonary food reserves resulting in slower accumulation of RDM, SDM and TDM culminating in a reduction of growth by a factor of 1.6 at 8 weeks. However, the SRR of inoculated plants was similar to that of control plants, suggesting that the balance between the root and shoot systems exists which is unchanged by the effect of the pathogen. CWC was decreased upon senescence to an average of 65% at abscission. The prevention of cotyledonary abscission in infected seedlings is suggested to be due in part to the CDM remaining above a critical level of 20% of the initial CDM. The implication of this response in relation to the infection biology of the pathogen is discussed.     

Effect of root formation on 14C-glycine uptake and incorporation into protein by attached and excised cotyledons of Helianthus annuus

Root formation was found to extend the life-span of excised cotyledons of Helianthus annuus L. markedly. Excised cotyledons of 12-day-old plants attained longer life-span, higher root number and total root length than cotyledons excised before or after 12 days. Protein content of attached cotyledons reached a maximum level 12 days after the commencement of germination followed by a decrease. Cotyledons excised 8 days after sowing showed maximum level of protein content 44 days after excision followed by a decrease. The increase was correlated with the full development of roots. The incorporation of ¹⁴C-glycine into protein followed a pattern similar to the protein content, both in attached and detached cotyledons.     

Appearance and disappearance of proteins in the shoot apical meristem of Sinapis alba in transition to flowering

Vegetative plants of Sinapis alba L. grown under short days were induced to flower by exposure to one long day or continuous long days. Irrespective of the number of long days, the first flower primordia were initiated by the shoot apical meristem 60 h after the start of the inductive treatment. An indirect histoimmunofluorescence technique was used to search in the apical meristem for three antigenic proteins which had been previously detected by immunodiffusion tests in the whole apical bud (Pierard et al. (1977) Physiol. Plant. 41, 254–258). One protein called protein A, present in the vegetative meristem, increased in concentration during the first 48 h following the start of the inductive treatment. It stayed constant up to 96 h and disappeared completely at a later time. Two other proteins called B and C, absent in the vegetative meristem, appeared in the meristem of induced plants between 30 and 36 h after the start of the inductive treatment and progressively accumulated at later times up to 240 h. These proteins appeared 8 h before the irreversible commitment of the meristem to produce flower primordia (point of no return) was reached and 24 h before start of flower production. These observations support an interpretation of floral evocation as consisting, at least partially, of an early and qualitative change in gene expression.Abbreviations AVB anti-vegetative-bud antiserum - ARB antireproductive-bud antiserum - IgG immunoglobulins G - TRITC tetramethylrhodamine isothiocyanate - GAR IgG goat antirabbit IgG - S₀ IgG non-immune rabbit IgG     

Priming of seeds with NaCl induces physiological changes in tomato plants grown under salt stress

The effects of seed priming with 6 M NaCl solution have been investigated with respect to growth and physiological responses of tomato plants ( Lycopersicon esculentum Mill. cv. Pera) exposed to 70 and 140 m M NaCl nutrient solutions from 11 to 60 days after sowing. Tomato seedlings from primed seeds emerged earlier than from non-primed seeds. At 70 m M , a lower shoot and root dry weight reduction was found in plants from primed seeds at the different harvests (30, 45 and 60 days after sowing), while at 140 m M the positive effect of seed priming was only shown in roots. Significant changes in Na⁺ and CI⁻ accumulation with seed priming were only found in roots at 60 days after sowing, with ion accumulation in roots being higher in plants grown at 70 and 140 m M from primed seeds. In leaves of salt-treated plants, significant increases in sugars and organic acids with seed priming were found from 30 days after sowing, and these increases were higher at longer treatment times. In roots, however, only the organic acids tended to increase in plants from primed seeds, although they increased less than in leaves, especially at 60 days after sowing. These results support the hypothesis that priming of seeds with NaCl induces physiological changes in the plants, changes which are shown more clearly at advanced growth stages.     

Indole acetic acid distribution coincides with vascular differentiation pattern during Arabidopsis leaf ontogeny

We used an anti-indole acetic acid (IAA or auxin) monoclonal antibody-based immunocytochemical procedure to monitor IAA level in Arabidopsis tissues. Using immunocytochemistry and the IAA-driven beta-glucuronidase (GUS) activity of Aux/IAA promoter::GUS constructs to detect IAA distribution, we investigated the role of polar auxin transport in vascular differentiation during leaf development in Arabidopsis. We found that shoot apical cells contain high levels of IAA and that IAA decreases as leaf primordia expand. However, seedlings grown in the presence of IAA transport inhibitors showed very low IAA signal in the shoot apical meristem (SAM) and the youngest pair of leaf primordia. Older leaf primordia accumulate IAA in the leaf tip in the presence or absence of IAA transport inhibition. We propose that the IAA in the SAM and the youngest pair of leaf primordia is transported from outside sources, perhaps the cotyledons, which accumulate more IAA in the presence than in the absence of transport inhibition. The temporal and spatial pattern of IAA localization in the shoot apex indicates a change in IAA source during leaf ontogeny that would influence flow direction and, consequently, the direction of vascular differentiation. The IAA production and transport pattern suggested by our results could explain the venation pattern, and the vascular hypertrophy caused by IAA transport inhibition. An outside IAA source for the SAM supports the notion that IAA transport and procambium differentiation dictate phyllotaxy and organogenesis.     

Influence of soil water deficits on root growth of cotton seedlings

Summary Cotton (Gossypium hirsutum L. cv. H14) seedlings were raised in soil of differing soil water content in specially designed pots in which the roots had access to freely available water and nutrients located 2.5 cm below the base of the soil core. The time for root emergence from the soil core and the rate of root growth were measured daily from sowing to harvest. The root and shoot dry weight and leaf water potential were measured at the final harvest 16 days after sowing. As soil water content decreased, the root emerged from the soil earlier and the initial rate of root elongation was faster. In spite of the availability of freely available water, the plants in the soil at low water contents had significantly lower leaf water potentials than those in soil at high water contents. The root: shoot ratio increased as the soil water content decreased. This arose from an absolute increase in root weight, with shoot weight not being significantly affected.     

Mobilization of Phosphorus in the Cotyledons of Young Seedlings of the Garden Pea (Pisum sativum L.)

Changes in the levels of various phosphorus fractions and ofphytase activity in the cotyledons of young pea seedlings grownin the light have been studied. It is shown that from the onsetof germination there is a lag of several days in the hydrolysisof phytic acid and that this is associated with a low levelof phytase activity in cotyledon extracts. Rapid developmentof phytase during the next few days is accompanied by a rapidincrease in the rate of phytic acid break-down and both reachmaximum levels after 6–7 days from soaking the seed. Theamount of phytic acid in the cotyledons becomes negligible afterabout 15 days and at the same time phytase activity declinesmarkedly. At this point protease activity is at a maximum andthe water content of the cotyledons begins to fall. Removal of the shoot 4 days after soaking the seed caused animmediate decrease in export of phosphorus from the cotyledonsbut did not affect the level of phytic acid for several days.Subsequently there was a small, but significant reduction inthe rate of phytic acid hydrolysis in de-shooted seedlings ascompared with intact plants in spite of the fact that phytaseactivity was not affected for several days. Similar effectswere observed when excised cotyledons were cultured on moistfilter-paper. Control mechanisms for phytic acid hydrolysis are discussedand it is concluded that regulation by the axis of the inorganicphosphate concentration at the sites of phytase activity maybe a means of controlling phytic acid hydrolysis.     

The transition to reproductive phase inchenopodium murale L. ecotype 197 - Early flowering long-day plant

Five days of suitable continuous light induced flowering in the majority ofChenopodium murale L. ecotype 197 plants as early as at the phase of the first pair of leaves. At the time of initiation of the 2nd to 4th pairs of leaves the capacity of plants to flower was reduced, the number of flowering plants being significantly lower under the same inductive light treatment. The capacity to flower increased again at the phase of the 5th and the 6th pairs of leaves. Inductive light treatment brought about a marked growth activation of organs present before induction, shoot apex elongation, precocious formation of new leaves and activation of axillary meristems. The course of these changes in plants of different age is demonstrated. The terminal flower developed during 5 short days following inductive light treatment. The paper shows similarities and differences between long-daymutale L. ecotype 197 and short-day C.rubrum L. ecotype 374 grown under practically uniform conditions.