Fruit ripening is a complex and highly coordinated developmental process involving the expression of many ripening-related genes under the control of a network of signalling pathways. The hormonal control of climacteric fruit ripening, especially ethylene perception and signalling transduction in tomato has been well characterized. Additionally, great strides have been made in understanding some of the major regulatory switches (transcription factors such as RIPENING-INHIBITOR and other transcriptional regulators such as COLOURLESS NON-RIPENING, TOMATO AGAMOUS-LIKE1 and ETHYLENE RESPONSE FACTORs), that are involved in tomato fruit ripening. In contrast, the regulatory network related to non-climacteric fruit ripening remains poorly understood. However, some of the most recent breakthrough research data have provided several lines of evidences for abscisic acid- and sucrose-mediated ripening of strawberry, a non-climacteric fruit model. In this review, we discuss the most recent research findings concerning the hormonal regulation of fleshy fruit ripening and their cross-talk and the future challenges taking tomato as a climacteric fruit model and strawberry as a non-climacteric fruit model. We also highlight the possible contribution of epigenetic changes including the role of plant microRNAs, which is opening new avenues and great possibilities in the fields of fruit-ripening research and postharvest biology.

Pollination of many flowers initiates a sequence of precisely regulated developmental events that include senescence of the perianth and development of the ovary. The plant hormone ethylene is known to play a key role in regulating the biochemical and anatomical changes that constitute the postpollination syndrome. For this reason, we have studied the pollination syndrome in Phalaenopsis orchids by examining the spatial and temporal location of ethylene biosynthesis within the orchid flower, and how this biosynthesis is regulated by factors that influence expression of genes that encode key enzymes in the ethylene biosynthetic pathway. In particular, we examined the role in the postpollination syndrome of the expression of the gene for l-aminocyclopropane-1-carboxylate (ACC) oxidase, which catalyzes the conversion of ACC to ethylene. In vivo incubation of tissues with the ethylene precursor ACC demonstrated that ACC oxidase activity increases after pollination in the stigma, contrary to the observation that activity is constitutive in petunia and carnation gynoecia. RNA blot hybridization of floral tissues indicates that the increase in ACC oxidase activity is due to de novo synthesis of mRNA and presumably protein, which is induced after pollination. Furthermore, the pattern of induction is consistent with a model of coordinate regulation of gene expression in which the pollination signal travels to other organs of the flower to induce their ethylene production. We have also used in situ hybridization to define further the temporal and spatial expression of ACC oxidase within the floral organs, showing that expression, and, by inference, the capability to oxidize ACC to ethylene, is induced in all living cells of the tissues examined after pollination. These findings contrast with work in petunia that suggests that ACC oxidase is localized to the stigmatic surface.It has been recognized for many years that pollination of flowers greatly accelerates senescence of nonessential floral organs such as the petals and sepals (Borochov and Woodson, 1989). Pollination of the flower results in an increase in ethylene production, which is thought to coordinate the senescence process and which may play a role in other aspects '

Low-salt barley plants contain low salt and high sugar levels; high-salt plants contain high salt but low sugar levels. It is shown that salt inhibits glucose transport into the cell and it is suggested that the low sugar level in high-salt plants is due to this inhibition. During uptake of salt by low -salt roots the sugar level falls, and rates of salt transport and respiration are both correlated with sugar level in the root. It is suggested that due to the high sugar level, rates of uptake of salt to low-salt roots may be exaggerated when compared with high-salt roots. The dependence on metabolic status has been ignored in kinetic studies of ion transport.

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Dark-grown pea seedlings (Pisum sativum L.) were irradiated for a short period each day with low intensity red light (662 nm), red light immediately followed by far red light (730 nm), or far red light alone. Other plants were transferred to a white light regime (14 hours light/10 hours dark). There was no change in the amount of RNA in the tissue on a fresh weight basis after the various treatinents. However, compared with dark-grown seedlings, those plants irradiated with red light showed an increase in the net RNA content per stem apex. In addition there was a two-to threefold increase in ribosomal RNA of the etioplasts relative to the total ribosomal RNA. These increases were comparable to those found in plants grown in the white light regime. The changes were much smaller if the dark-grown plants were irradiated either with red light followed by far red light, or with far red light alone. Thus continuous light is not essential for the production of ribosomal RNA in plastids, and the levels of ribosomal RNA found in chloroplasts can also be attained in etioplasts of pea leaves in the dark provided the leaf phytochrome is maintained in its active form.Evidence from several laboratories has shown that phytochrome mediates in photoregulating the synthesis of chloroplast proteins (3,5,(13)(14)(15)19). Thus activation of the phytochrome system in dark-grown pea seedlings by a brief irradiation with red light results in a marked increase in the synthesis of ribulose-1 ,5-diphosphate carboxylase and other chloroplast enzymes in the dark (3,19). Continuous light then is not required for the synthesis of Calvin cycle enzymes, nor is it required for svnthesis of enzymes of the C4-dicarboxylic acid pathway of photosynthesis (4).At least some of these chloroplast proteins appear to be synthesized on chloroplast ribosomes (17,19,20), but it is not known whether the phytochrome-mediated increase in plastid protein synthesis involves an increase in the number of plastid ribosomes or whether these ribosomes are already present in the etioplasts of dark-grown plants. Continuous light is known to increase the amount of plastid rRNA (1,8,22) and also plastid RNA polymerase (2) In the experiments reported here, we have measured the amount of plastid and cytoplasmic rRNA in the apices of darkgrown pea seedlings and in seedlings subjected to various light regimes. The leaves of dark-grown seedlings contained lower amounts of chloroplast-type rRNA (16 S and 23 S) compared with green leaves, but after irradiating the seedlings with light at 662 nm for short periods, the 16 S and 23 S RNA increased to the levels found in the leaves of green plants of the same chronological age. MATERIALS AND METHODSPea seeds (Pisum sativum L., cv Greenfeast, obtained from Yates Seed Co., Sydney) which had not been treated with fungicide or preservatives were used. The seeds were washed in a dilute solution of detergent (1% Teepol, Shell Chemical Co.), soaked in 3% (v/v) Chlorize (Nightingale Chemical Co., Sydney) for 15 min and then washed...