MULTI-SEASONAL VS INTRA-SEASONAL STRUCTURAL CHANGES IN GRAPEVINE: A COMPLEX STRESS RESPONSE
Grapevine is an economically important crop, which serves as a model plant for ecophysiological responses to water stress. While moderate water stress is needed in order to achieve premium wine quality, high stress is harmful and may cause permanent damage to the plants. Water availability influences the water status, among other things, by changing the hydraulic anatomy of the grapevine (Munitz et al., 2018). In the structure-function context of plant-water relations, the cell wall architecture and composition is extremely important (Shtein et al., 2018). Current study explores the dynamic effects of the intra-seasonal water availability on morphological changes, hydraulic anatomy and cell wall composition.
The research was conducted on a commercial mature vineyard planted with Vitis vinifera cv. ‘Cabernet Sauvignon’. Three water availability treatments were investigated: 1) Non-stressed control: intensively irrigated grapevines grown in drainage lysimeters, with a surplus of water supply (irrigation every hour). 2) Mild water stress treatment: irrigation was initiated with the beginning of bud-break. 3) Severe water stress treatment: irrigation began only when the values of stem water potential reached -1.2 MPa. For the investigation of intra-seasonal dynamic stress, leaf petioles were sampled on three dates during the growth season. Hydraulic anatomy were examined by light microscopy and image analysis. Cell wall components was examined both by conventional histology and by immunohistochemical staining, viewed under confocal microscope.
At the beginning of the season, surprisingly, severe drought stress lead to diverse morphological and anatomical changes, though the stem water potential was not low. These changes included: shorter petioles, reduction of vessel diameter and increased vessel density, and changes in the cell wall composition. The cell wall compositional changes indicated increased level of biomechanically important components: more lignin and increase in pectic homogalacturonans methyl-esterification. As the season progressed, similar changes occurred in all of the treatments regardless of water availability.
Apparently, perennial water status influences the plant structure and function already at the beginning of the next season. However, intra-seasonally, the structure becomes independent of the water status. Temperature is a strong determinator of the plant structure, and we assume it’s the main intra-seasonal influencing factor in current study. The changes in methyl-esterification of homogalacturonans are especially interesting, as they suggest that enzymatic activity takes part in grapevine stress response, and opens new questions about the mechanical, protective role of pectic homogalacturonans in particular and cell walls in general.
Munitz S, Netzer Y, Shtein I, Schwartz A. 2018. Water availability dynamics have long- term effects on mature stem structure in Vitis vinifera. American Journal of Botany 105: 1–10.
Shtein I, Bar-On B, Popper ZA. 2018. Plant and algal structure: from cell walls to biomechanical function. Physiologia Plantarum 164: 56–66.