Tomato fruit photosynthesis is seemingly unimportant in primary metabolism and ripening but plays a considerable role in seed development

Fruit of tomato (Solanum lycopersicum), like those from many species, have been characterized to undergo a shift from partially photosynthetic to truly heterotrophic metabolism. While there is plentiful evidence for functional photosynthesis in young tomato fruit, the rates of carbon assimilation rarely exceed those of carbon dioxide release, raising the question of its role in this tissue. Here, we describe the generation and characterization of lines exhibiting a fruit-specific reduction in the expression of glutamate 1-semialdehyde aminotransferase (GSA). Despite the fact that these plants contained less GSA protein and lowered chlorophyll levels and photosynthetic activity, they were characterized by few other differences. Indeed, they displayed almost no differences in fruit size, weight, or ripening capacity and furthermore displayed few alterations in other primary or intermediary metabolites. Although GSA antisense lines were characterized by significant alterations in the expression of genes associated with photosynthesis, as well as with cell wall and amino acid metabolism, these changes were not manifested at the phenotypic level. One striking feature of the antisense plants was their seed phenotype: the transformants displayed a reduced seed set and altered morphology and metabolism at early stages of fruit development, although these differences did not affect the final seed number or fecundity. Taken together, these results suggest that fruit photosynthesis is, at least under ambient conditions, not necessary for fruit energy metabolism or development but is essential for properly timed seed development and therefore may confer an advantage under conditions of stress.     

柑橘果实的光合特性、产物运输及分配在糖分积累中的作用

测定了温州蜜柑 (CitrusunshiuMarc .cv .Miyagawawase)果实发育进程中干鲜重、果皮光合速率和叶绿素含量的变化 ,并用14 CO2 示踪技术研究了果皮和叶同化生成的光合产物在果实内的运输分配特性。结果表明 :果皮光合速率与叶绿素含量有关 ,随着叶绿素含量的下降 ,果实光合速率也快速下降。在果实完熟之前 ,即使是当果皮积累的干重超过汁囊时 ,叶同化产物仍主要分配到汁囊中 ;而在完熟阶段 ,果皮光合速率接近零 ,果皮成了叶同化产物的主要库。果皮的同化产物 ,主要保留在果皮中 ,输入到汁囊的比率随果实发育而下降 ,但高峰时也有 12 %输入汁囊。与对照相比 ,果实遮光处理后降低了果皮与汁囊的干重和含糖量。上述结果表明果皮光合产物主要用于果皮自身的发育并能减少对叶光合产物的依赖 ,同时也能部分增加汁囊糖的积累     

In vitro growth and ripening of strawberry fruit in the presence of ACC, STS or propylene

Strawberry ( Fragaria ananassa Duch.) fruit exhibit limited capacity for continued development following harvest. This problem can be circumvented by maintaining harvested strawberry fruit in solutions containing sucrose and a bactericide. In this study, we investigated the respiratory and ethylene production kinetics and ethylene responsiveness in strawberry fruit harvested immature and ripened in vitro in the presence of propylene. The effects of 1-amino-cyclopropane-1-carboxylic acid (ACC) and silver thiosulfate (STS) alone and in combination were also examined. Respiration and ethylene patterns of fruit harvested green and developed in vitro declined with maturation and ripening, as did those of field-grown fruit harvested at different stages of ripeness. Exposure of detached green strawberry fruit to 5000 μl litre^-1 propylene failed to stimulate respiration or ethylene production, but advanced pigmentation changes and fresh-weight gain significantly. Excised fruit provided with 1 mol^-3 ACC exhibited increased ethylene production, enhanced fresh-weight gain, and accelerated anthocyanin accumulation, but showed no change in respiration. The developmental response of harvested strawberry fruit to propylene or ACC was dependent on fruit maturity at harvest, with white fruit exhibiting greater insensitivity compared with green fruit. Silver thiosulfate (0.5 mol^-3) applied alone or in combination with ACC failed to delay ripening in excised strawberry fruit. These experiments demonstrate that ripening in detached strawberry fruit can be modified by ethylene only in green fruit that are provided with a carbohydrate source. Ethylene, when applied exogenously as ACC or propylene to green fruit, can slightly increase fruit growth and the rate of colour development.     

Ascorbic acid metabolism during bilberry (Vaccinium myrtillus L.) fruit development

Bilberry (Vaccinium myrtillus L.) possesses a high antioxidant capacity in berries due to the presence of anthocyanins and ascorbic acid (AsA). Accumulation of AsA and the expression of the genes encoding the enzymes of the main AsA biosynthetic route and of the ascorbate-glutathione cycle, as well as the activities of the enzymes involved in AsA oxidation and recycling were investigated for the first time during the development and ripening of bilberry fruit. The results showed that the AsA level remained relatively stable during fruit maturation. The expression of the genes encoding the key enzymes in the AsA main biosynthetic route showed consistent trends with each other as well as with AsA levels, especially during the first stages of fruit ripening. The expression of genes and activities of the enzyme involved in the AsA oxidation and recycling route showed more prominent developmental stage-dependent changes during the ripening process. Different patterns of activity were found among the studied enzymes and the results were, for some enzymes, in accordance with AsA levels. In fully ripe berries, both AsA content and gene expression were significantly higher in skin than in pulp.     

Acid Phosphatase Development during Ripening of Avocado

The activity and subcellular distribution of acid phosphatase were assayed during ethylene-induced ripening of whole fruit or thick slices of avocado (Persea americana Mill. var. Fuerte and Hass). The activity increased up to 30-fold during ripening in both the supernatant fraction and the Triton X-100 extract of the precipitate of a 30,000g centrifugation of tissue homogenates from whole fruit or slices ripening in moist air. Enzyme activity in the residual precipitate after Triton extraction remained constant. The development of acid phosphatase in thick slices ripened in moist air was similar to that in intact fruit, except that enzyme development and ripening were accelerated about 24 hours in the slices. The increase in enzyme activity that occurs in slices ripening in moist air was inhibited when tissue sections were infiltrated with solutions, by aspiration for 2 minutes or by soaking for 2 hours, anytime 22 hours or more after addition of ethylene. This inhibition was independent of the presence or absence of cycloheximide or sucrose (0.3-0.5m). However, the large decline in enzyme activity in the presence of cycloheximide, as compared with the controls, indicated that synthesis of acid phosphatase was occurring at all stages of ripening.     

Characterisation of an alpha-galactosidase with potential relevance to ripening related texture changes

alpha-Galactosidase (EC 3.2.1.22) from ripe papaya (Carica papaya L.) fruit was fractionated by a combination of ion exchange and gel filtration chromatography into three forms, viz., alpha-galactosidase 1, 2 and 3. The predominant isoform, alpha-gal 2, was probably a tetramer with a native molecular mass of about 170 kDa and 52 kDa-sized subunits and an estimated pI of 7.3. The subunit's N-terminal amino acid sequence shared high identity (97%) with the deduced sequence of a papaya cDNA clone encoding a putative alpha-galactosidase PAG2 as well as with an Ajuga reptans L. GGT1 clone encoding a galactan: galactan galactosyltransferase (66%). During ripening, alpha-galactosidase activity increased concomitantly with firmness loss and this increase was largely ascribed to alpha-gal 2. The protein level of alpha-gal 2 as estimated by immunoblot was low in developing fruits and generally increased with ripening. alpha-Galactosidase 2 also had the ability to markedly catalyse increased pectin solubility and depolymerisation while the polymers were still structurally attached to the cell walls mimicking, in part, the changes that occur during ripening. The close correlation between texture changes, alpha-gal 2 activity and protein levels as well as capability to modify intact cell walls suggest that the enzyme might contribute to papaya fruit softening during ripening. The purported mechanism of alpha-gal 2 action as a softening enzyme was discussed in terms of its functional capacity as a glycanase or perhaps, as a transglycosylase.     

Cloning of FaPAL6 gene from strawberry fruit and characterization of its expression and enzymatic activity in two cultivars with different anthocyanin accumulation

The accumulation of anthocyanin pigments is one of the most important traits that turn strawberry fruit attractive to consumers. During ripening, strawberry fruit color development is associated to anthocyanin synthesis through the phenylpropanoid pathway. Phenylalanine ammonia-lyase (PAL) is a key enzyme in this pathway, having a determining role in strawberry fruit quality. In this work, we studied the level of anthocyanins during fruit ripening of two cultivars that differ in color development (Camarosa and Toyonoka). Toyonoka showed a lower anthocyanin accumulation that was limited to external fruit tissue, while Camarosa accumulated higher amount of anthocyanins in both internal and external sections. In addition, we cloned a full-length gene (FaPAL6) and analyzed its expression in different strawberry plant tissues. The expression of this gene is fruit specific, and increases during fruit ripening in both cultivars along with anthocyanin accumulation. The mRNA level of FaPAL6 was higher in Camarosa. PAL enzyme activity increased at similar rates in both cultivars at early ripening stages, but at the end of ripening PAL activity diminished in Toyonoka while it rose markedly in Camarosa. PAL activity was higher in internal fruit tissue, showing no correlation with anthocyanin level of the same section in both cultivars. The higher FaPAL6 expression and activity detected in Camarosa could be associated to the enhanced anthocyanin accumulation found in this cultivar.     

Proanthocyanidin synthesis and expression of genes encoding leucoanthocyanidin reductase and anthocyanidin reductase in developing grape berries and grapevine leaves

Proanthocyanidins (PAs), also called condensed tannins, can protect plants against herbivores and are important quality components of many fruits. Two enzymes, leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR), can produce the flavan-3-ol monomers required for formation of PA polymers. We isolated and functionally characterized genes encoding both enzymes from grapevine (Vitis vinifera L. cv Shiraz). ANR was encoded by a single gene, but we found two highly related genes encoding LAR. We measured PA content and expression of genes encoding ANR, LAR, and leucoanthocyanidin dioxygenase in grape berries during development and in grapevine leaves, which accumulated PA throughout leaf expansion. Grape flowers had high levels of PA, and accumulation continued in skin and seeds from fruit set until the onset of ripening. VvANR was expressed throughout early flower and berry development, with expression increasing after fertilization. It was expressed in berry skin and seeds until the onset of ripening, and in expanding leaves. The genes encoding LAR were expressed in developing fruit, particularly in seeds, but had low expression in leaves. The two LAR genes had different patterns of expression in skin and seeds. During grape ripening, PA levels decreased in both skin and seeds, and expression of genes encoding ANR and LAR were no longer detected. The results indicate that PA accumulation occurs early in grape development and is completed when ripening starts. Both ANR and LAR contribute to PA synthesis in fruit, and the tissue and temporal-specific regulation of the genes encoding ANR and LAR determines PA accumulation and composition during grape berry development.     

Responses of strawberry fruit to 1-Methylcyclopropene (1-MCP) and ethylene

1-Methylcyclopropene (1-MCP), a competitive inhibitorof ethylene action, binds to the ethylene receptor toregulate tissue responses to ethylene. In this work,we investigated the effects of 1-MCP and exogenousethylene on ripening, respiration rate, ionicconductivity and peroxidase activity in strawberryfruit. Strawberry fruit can ripen without exogenousethylene treatment, but exogenous ethylene inducessecondary ripening processes. Results indicated thatstimulation of respiration by ethylene wasdose-dependent. Fruit colour development and softeningwere slightly accelerated by ethylene, but changes insoluble solid content were not. 1-MCP may/may notaffect the respiratory rise induced by exogenousethylene dependent on fruit maturity. Cycloheximide(CHI) reduced the ethylene-induced respiratoryincrease. Combinations of 1-MCP and CHI reducedrespiration more than CHI alone. 1-MCP and CHI did notinfluence the primary respiratory change in nonethylene-treated fruit. This indicates that ethyleneinduced respiratory increase may involve an ethylenereceptor in early harvested fruit, but not in laterharvested fruit. Exogenous ethylene stimulatedrespiration by regulating new respiratory enzyme(s)synthesis in strawberry fruit. Ethylene induced anionic leakage increase, and this was positivelycorrelated to fruit water loss and peroxidaseactivity. These results suggest that non-climactericfruit, such as strawberry, may have different ethylenereceptor(s) and/or ethylene receptor(s) may havedifferent regulatory functions. It may be thesecondary effect of ethylene to stimulate respirationin strawberry. Non-climacteric fruit ripening may berelated to the development of active oxygen species(AOS) induced by postharvest stress.     

Changes in gene expression during strawberry fruit ripening and their regulation by auxin

Changes in messenger RNA during the development of the strawberry (Fragaria ananassa Duch.), a non-climacteric fruit, were analysed by extracting total RNA and separating the in-vitro translated products by two-dimensional polyacrylamide gel electrophoresis. Alterations in numerous messenger RNAs accompanied fruit development between the immature green stage and the overripe stage, with prominent changes detected at or before the onset of ripening. A number of messenger RNAs undetectable in immature green fruit increased as the fruit matured and ripened. Others showed a marked decrease in advance of the ripening phase. A further group of messenger RNAs was prominent in immature and ripe fruit but absent just prior to the turning stage. Removing the achenes from a segment of the fruit accelerated anthocyanin accumulation in the de-achened portion and produced a pattern of translated polypeptides similar to normal ripe fruit. Application of the synthetic auxin 1-naphthaleneacetic acid to the de-achened receptacle produced a translation pattern similar to that in mature green fruit. These findings indicate that ripening in strawberry is associated with the expression of specific genes.     

NaHSO3对桃树的生理效应及产量、品质的影响

于桃树果实膨大期喷施100ppm NaHSO3可获得增产、优质、早熟的效果。此与NaHSO3能增加叶绿素含量、提高光合速率、比叶重、促进希尔反应,抑制硝酸还原酶、过氧化氢酶活性,增加单果重等多重生理效应相关。     

Sexual dimorphism and seasonal changes of leaf gas exchange in the dioecious tree Ilex paraguariensis grown in two contrasted cultivation types

Yerba maté (Ilex paraguariensis, Aquifoliaceae) is a subtropical, evergreen, dioecious, South American tree. In one preliminary study, it was observed that the functional strategy of yerba mate females, aiming to finish reproductive process, was increased transpiration relative to photosynthetic rates compared with males, on self‐shaded leaves. We hypothesised that the long‐term gas exchange response of males and females can evolve independently of phenological stage and cultivation type. In this spirit, the primary aim of the study was to analyse the physiological sexual dimorphism of this species, evaluating fluctuations of gas exchanges related to microclimate and phenological stages. A field study was conducted on adult plants of yerba maté cultivated in monoculture (MO) and in forest understorey (FUS), and measurements carried out in situ on microclimate and leaf gas exchange parameters. The photosynthetic photon flux density that was attained at leaf level in FUS was reduced roughly 10‐fold compared with that in MO. Various leaf age populations were observed during a 2‐year period at 2‐month intervals and grouped into four categories: young, young‐fully‐expanded, fully‐expanded and old. Young and young‐fully‐expanded leaves were the most active in photosynthesis. Leaves of female plants showed greater photosynthetic rate than those of male plants, which was expressed on all leaf age categories in MO, but only during vegetative stages previous to flowering and fruit ripening. The photosynthesis of young‐fully‐expanded leaves of females grown in FUS was superior to males but only during winter growth pause. The stomatal conductance differed in relation to cultivation type and leaf age but did not show the sexual differentiation. Physiological sexual dimorphism in yerba mate is shown to be plastic, responding to environmental conditions. The cost associated to the reproduction of yerba maté could be most easily met showing physiological differentiation of both sexes. A higher reproductive investment of females might be compensated for by exhibiting greater leaf photosynthesis than males that occurs in vegetative stages that precede flowering and fruit ripening.     

NaHSO3对桃树的生理效应及产量品质的影响

于桃树果实膨大期喷施１００ｐｐｍ ＮａＨＳＯ２可获得增产、优质、早熟的效果。此与ｎａＨＳＯ２能增加叶绿素含量、提高光合速率、比叶重、促进希尔反应,抑制硝酸还原酶、过氧氢酶活性,增加单果重等多重生理效应相关。