Plant growth control by water deficit: which process(es) to lead the game?
Résumé
The nature of plant growth limitation by environmental stresses such as water deficit is a central question for physiologists and breeders because this knowledge could help to target key processes for breeding programs and help designing plants able to maintain growth under stressful conditions. In order to grow, plant cells must loosen their walls, absorb water, reduce and process enough C and minerals to match the plant demand. Therefore, plant cell growth can be limited by cell wall rheological properties, cell or tissue hydraulics or by metabolism. In addition, cell division can be an important process to consider as cell number, together with cell size, contributes to the whole organ size. Over the past few years, our group has questioned the importance of these limitations using combinations of ecophysiological tools, spatio-temporal growth analysis and modelling in ranges of genotypes (including natural variants and mutants). Among the outcomes of these studies, I will show that (i) hydraulic limitation plays a great role on organ growth on the short term, (ii) distinct members of the cell wall loosening expansins family are downstream, unspecific targets of a range of converging developmental, genetic, and environmental cues (iii) metabolism and growth are tightly connected, possibly through a remote control of leaf expansion by starch metabolism and (iv) leaf cell size is more a consequence of growth control at higher levels of organization than vice-versa