Inflorescence of grapevine (Vitis vinifera L.): a high ability to distribute its own assimilates.

The distribution of carbon (C) into whole grapevine fruiting cuttings was investigated during flower development to determine the relative contribution of inflorescence and leaf photoassimilates in the total C balance and to investigate their partitioning towards other plant organs. A (13)C labelling procedure was used to label C photoassimilates by leaves and inflorescences in grapevine. Investigations were carried out at various stages of flower/berry development, from separated cluster to fruit set, using grapevine fruiting cuttings with four leaves (Vitis vinifera L. cv. Chardonnay). This is the first study reporting that, during its development, (i) the carbon needs of the inflorescence were met by both leaf and inflorescence photosynthesis, and (ii) the inflorescence amazingly participated significantly to the total C balance of grapevine cuttings by redistributing an important part of its own assimilates to other plant organs. With regard to flowering, 29% of C assimilated by the inflorescence remained in the inflorescence, while partitioning towards the stem reached 42% and, as a lower proportion, 15% in leaves, and 14% in roots.

Botryticides affect grapevine leaf photosynthesis without inducing defense mechanisms.

The effects of the two botryticides, fludioxonil (fdx) and fenhexamid (fhd), were investigated on grapevine leaves (Vitis vinifera L. cv. Pinot noir) following photosynthesis and defense mechanisms. Treatments were carried out in vineyard at the end of flowering. Phytotoxicity of both fungicides was evaluated by measuring variations of leaf photosynthetic parameters and correlated expression of photosynthesis-related genes. Results demonstrated that similar decrease in photosynthesis was caused by fdx and fhd applications. Moreover, the mechanism leading to photosynthesis alteration seems to be the same for both fungicides. Stomatal limitation to photosynthetic gas exchange did not change following treatments indicating that inhibition of photosynthesis was mostly attributed to non-stomatal factors. Nevertheless, fungicides-induced depression of photosynthesis was related neither to a decrease in Rubisco carboxylation efficiency and in the capacity for regeneration of ribulose 1,5-bisphosphate nor to loss in PSII activity. However, fdx and fhd treatments generated repression of genes encoding proteins involved in the photosynthetic process. Indeed, decreased photosynthesis was coupled with repression of PsbP subunit of photosystem II (psbP1), chlorophyll a/b binding protein of photosystem I (cab) and Rubisco small subunit (rbcS) genes. A repression of these genes may participate in the photosynthesis alteration. To our knowledge, this is the first study of photosynthesis-related gene expression following fungicide stress. In the meantime, defense responses were followed by measuring chitinase activity and expression of varied defense-related genes encoding proteins involved in phenylpropanoid synthesis (PAL) or octadecanoid synthesis (LOX), as well as pathogenesis-related protein (Chi4C). No induction of defense was observed in botryticides-treated leaves. To conclude, the photosynthesis is affected without any triggering of plant defense responses.

Barley anther culture: assessment of carbohydrate effects on embryo yield, green plant production and differential plastid development in relation with albinism.

Sugars and polyols were tested at different steps of anther culture in barley (Hordeum vulgare L.) to elucidate their influence on both the overall yield of androgenesis and the structure of plastids in relation to albinism. During the pretreatment period, the osmotic regulation in the medium was beneficial to microspore embryogenesis regardless of the type and concentration of the tested osmoticum. The use of mannitol (300 mOsm/kg), sorbitol (180 mOsm/kg), PEG (240 mOsm/kg) and sucrose (180 mOsm/kg) gave the best results in terms of green plant production, although the influence of each substance differed according to the studied parameter. Similarly, during anther culture the regulation of the osmotic pressure in the medium had various effects, according to the osmoticum used. The best results were obtained using mannitol (364 mOsm/kg), providing 139.7 green plants per 100 plated anthers. Plastids were examined by electron microscopy following both pretreatment and culture. In the presence of mannitol and PEG, plastids did not accumulate starch at any stage of the protocol but they started to differentiate into chloroplasts in the microspore-derived embryos. Using sorbitol and sucrose, plastids differentiated poorly but accumulated large amounts of starch, suggesting that these sugars are metabolized by micropores and microspore derived structures. However, the accumulation of starch was not correlated with the occurrence of albinism. These results indicated that, in barley, the osmotic regulation was favourable to switch the microspore gametophytic program toward a sporophytic program regardless of the nature of the osmoticum. In addition, during the pretreatment period, mannito was found to be the most suitable osmoticum for subsequent embryo development.