COMPARATIVE EFFECTS OF GIBBERELLIN AND INDOLE COMPOUNDS ON THE INDUCTION OF PARTHENOCARPY IN SEXUALLY INCOMPATIBLE PERESKIA ACULEATA

Sachar , R. C. (U. Delhi, India.) Comparative effects of gibberellin and indole compounds on the induction of parthenocarpy in sexually incompatible Pereskia aculeata. Amer. Jour. Bot. 49(9): 913–917. Illus. 1962.—The effects of indoleacetic acid (IAA), indolebutyric acid (IBA), gibberellin (G) and gibberellic acid (GA) were studied on the fruit growth of the sexually incompatible Pereskia. Under natural conditions, this plant did not produce any fruits and seeds, and the flowers abscised a week after anthesis. IAA (50–500 ppm) delayed the formation of an abscission layer by another 2 weeks, but it was ineffective in inducing parthenocarpy. IBA (50–500 ppm) induced fruit-set in only 15% of the flowers. Best response was achieved by G (100–500 ppm), or GA (100–500 ppm), which gave 100% fruit-set. The effect of GA in inducing parthenocarpy was not inhibited when used in conjunction with IAA. Maximum size of the fruits was obtained with 2 sprayings of GA, and subsequent sprays were of no consequence. Further, fruit size was the largest when GA or G was sprayed at anthesis, or on old flower buds, but it was much less when the chemicals were sprayed on young flower buds. There was no stimulation of the growth of ovules; instead, a translucent mucilaginous placental tissue developed within the cavity of the fruit wall. Attempts were made to culture ovules and the placental tissue on artificial nutrient medium, but without success.     

Self‐pollination and parthenocarpic ability in developing ovaries of self‐incompatible Clementine mandarins (Citrus clementina)

This study aimed to determine if self‐pollination is needed to trigger facultative parthenocarpy in self‐incompatible Clementine mandarins (Citrus clementina Hort. ex Tan.). ‘Marisol’ and ‘Clemenules’ mandarins were selected, and self‐pollinated and un‐pollinated flowers from both cultivars were used for comparison. These mandarins are always seedless after self‐pollination and show high and low ability to develop substantial parthenocarpic fruits, respectively. The time‐course for pollen grain germination, tube growth and ovule abortion was analyzed as well as that for carbohydrates, active gibberellins (GA₁ and GA₄), auxin (IAA) and abscisic acid (ABA) content in the ovary. ‘Clemenules’ showed higher pollen grain germination, but pollen tube development was arrested in the upper style 9 days after pollination in both cultivars. Self‐pollination did not stimulate parthenocarpy, whereas both un‐pollinated and self‐pollinated ovaries set fruit regardless of the cultivar. On the other hand, ‘Marisol’ un‐pollinated flowers showed greater parthenocarpic ovary growth than ‘Clemenules’ un‐pollinated flowers, i.e. higher ovule abortion rate (+21%), higher fruit set (+44%) and higher fruit weight (+50%). Further, the greater parthenocarpic ability of ‘Marisol’ paralleled higher levels of GA₁ in the ovary (+34% at anthesis). ‘Marisol’ ovary also showed higher hexoses and starch mobilization, but lower ABA levels (?64% at anthesis). Self‐pollination did not modify carbohydrates or GA content in the ovary compared to un‐pollination. Results indicate that parthenocarpy in the Clementine mandarin is pollination‐independent with its ability to set depending on the ovary hormone levels. These findings suggest that parthenocarpy in fertile self‐incompatible mandarins is constitutively regulated.     

Cytokinin-Induced Parthenocarpic Fruit Development in Tomato Is Partly Dependent on Enhanced Gibberellin and Auxin Biosynthesis

Fruit set of plants largely depends on the biosynthesis and crosstalk of phytohormones. To date the role of cytokinins (CKs) in the fruit development is less understood. Here, we showed that parthenocarpic fruit could be induced by 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU, an active CK) in tomato ( Solanum lycopersicum cv. Micro-Tom). The fresh weight of CPPU-induced parthenocarpic fruits was comparable with that induced by GA₃. Importantly, CPPU-induced parthenocarpy was found to be compromised by simultaneous application of paclobutrazol (a GA biosynthesis inhibitor), and this effect could be restored by exogenous GA₃. Like pollination, CPPU-induced fruit showed enhanced accumulation of GA₁₊₃ and indole-3-acetic (IAA), which were accompanied by elevated expression of GA biosynthesis genes like SlGPS, SlGA20ox1, SlGA20ox2 and SlGA3ox1, and IAA biosynthesis gene ToFZY. Elevated GAs level in CPPU-induced fruits was also associated with down-regulation of GA inactivation genes, namely SlGA2ox1,2,3,4,5 in comparison with untreated control. These results suggested that CKs may induce parthenocarpy in tomato partially through modulation of GA and IAA metabolisms.     

2,4‐D‐induced parthenocarpy in pear is mediated by enhancement of GA4 biosynthesis

Parthenocarpy, the productions of seedless fruit without pollination or fertilization, is a potentially desirable trait in many commercially grown fruits, especially in pear, which is self‐incompatible. Phytohormones play important roles in fruit set, a process crucial for parthenocarpy. In this study, 2,4‐dichlorophenoxyacetic acid (2,4‐D), an artificially synthesized plant growth regulator with functions similar to auxin, was found to induce parthenocarpy in pear. Histological observations revealed that 2,4‐D promoted cell division and expansion, which increased cortex thickness, but the effect was weakened by paclobutrazol (PAC), a gibberellin (GA) biosynthesis inhibitor. Phenotypic differences in pear may therefore be due to different GA contents. Hormone testing indicated that 2,4‐D mainly induced the production of bioactive GA₄, rather than GA_3. Three key oxidase genes function in the GA biosynthetic pathway: GA20ox, GA3ox and GA2ox. In a pear group treated with only 2,4‐D, PbGA20ox2‐like and PbGA3ox‐1 were significantly upregulated. When treated with 2,4‐D supplemented with PAC, however, expression levels of these genes were significantly downregulated. Additionally, PbGA2ox1‐like and PbGA2ox2‐like expression levels were significantly downregulated in pear treated with either 2,4‐D only or 2,4‐D supplemented with PAC. We thus hypothesize that 2,4‐D can induce parthenocarpy by enhancing GA₄ biosynthesis.     

Molecular dissection of the role of auxin in fruit initiation

Fruit set and growth usually requires fertilization. Fruit set and development without fertilization is called parthenocarpy. Feeding auxin to virgin flowers induces fruit development without fertilization. Recent studies by Hua Wang et al. and Marc Goetz et al. have identified molecular events leading to fruit initiation in the absence of fertilization, showing that parthenocarpy can be achieved by altering different steps of the auxin signaling pathway. Thus, independent evidence indicates that auxin plays a key role in fruit initiation.     

转基因技术生产无籽果实的新策略

无籽果实具有许多优点 ,深受人们喜爱。传统无籽果实生产方法存在着诸如单性结实品种少、外用激素施用量不易掌握及四倍体品种较难获得等一系列问题。分子遗传研究表明 ,植物基因组中含有影响单性结实的基因 ,某些来自于细菌的基因也可在植物激素生物合成途径中起调节作用。应用这些目的基因 ,已建立了转基因生产无籽果实的新策略 ,如在种皮或子房特异性启动子控制下的生长素基因或细胞毒素基因的表达及“终止子”技术的运用等 ,这将大规模地促进蔬菜和水果生产 ,提高果蔬产品的市场价值。     

转基因技术生产无籽果实的新策略

无籽果实具有许多优点,深受人们喜爱。传统无籽果实生产方法存在着诸如单性结实品种少、外用激素施用量不易掌握及四倍体品种较难获得等一系列问题。分子遗传研究表明,植物基因组中含有影响单性结实的基因,某些来自于细菌的基因也可在植物激素生物合成途径中起调节作用。应用这些目的基因,已建立了转基因生产无籽果实的新策略,如在种皮或子房特异性启动子控制下的生长素基因或细胞毒素基因的表达及“终止子”技术的运用等,这将大规模地促进蔬菜和水果生产,提高果蔬产品的市场价值。     

Pollen Morphology and Boron Concentration in Floral Tissues as Factors Triggering Natural and GA-Induced Parthenocarpic Fruit Development in Grapevine

Parthenocarpic fruit development (PFD) reduces fruit yield and quality in grapevine. Parthenocarpic seedless berries arise from fruit set without effective fertilization due to defective pollen germination. PFD has been associated to micronutrient deficiency but the relation of this phenomenon with pollen polymorphism has not been reported before. In this work, six grapevine cultivars with different tendency for PFD and grown under micronutrient-sufficient conditions were analyzed to determine pollen structure and germination capability as well as PFD rates. Wide variation in non-germinative abnormal pollen was detected either among cultivars as well as for the same cultivar in different growing seasons. A straight correlation with PFD rates was found (R² = 0.9896), suggesting that natural parthenocarpy is related to defective pollen development. Such relation was not observed when PFD was analyzed in grapevine plants exposed to exogenous gibberellin (GA) or abscissic acid (ABA) applications at pre-anthesis. Increase (GA treatment) or reduction (ABA treatment) in PFD rates without significative changes in abnormal pollen was determined. Although these plants were maintained at sufficient boron (B) condition, a down-regulation of the floral genes VvBOR3 and VvBOR4 together with a reduction of floral B content in GA-treated plants was established. These results suggest that impairment in B mobility to reproductive tissues and restriction of pollen tube growth could be involved in the GA-induced parthenocarpy.     

Induced parthenocarpy-a way of manipulating levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 2. Diffusible hormones

Indol-3-acetic acid (IAA), gibberellin-like substances (GAs), and abscisic acid (ABA) were measured throughout the first 35 days of fruit development in agar diffusates from seeded and parthenocarpic tomato fruits. Parthenocarpic fruit growth was induced with either an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃). IAA and GAs were at their highest levels in diffusates during the early stages of fruit growth, whereas diffusible ABA increased later. Most IAA was found in diffusates from auxin-induced and seeded fruits, whereas GAs were at their lowest levels in seeded fruits. There were only minor differences in ABA concentrations regardlesss of the treatments.Levels of diffusible hormones of tomato fruits may be easily manipulated by inducing parthenocarpic fruit growth. In spite of no obvious relationship between fruit growth and hormone levels in this study, induced parthenocarpy is considered a useful tool to further elucidate the role of hormones in fruit development and sink-source interactions.