Turgor‐time controls grass leaf elongation rate and duration under drought stress

• Published in: Plant, cell and environment cell and environment, 2021-05, Vol.44 (5), p.1361-1378
• Main Authors: Coussement, Jonas R., Villers, Selwyn L. Y., Nelissen, Hilde, Inzé, Dirk, Steppe, Kathy
• Format: Article
• Language: English
• Subjects: Cell differentiation; division; Drought; drought stress; Elongation; grass; Grasses; Growth models; Growth patterns; leaf elongation rate; leaf kinetics; Leaves; mechanistic model; Ontogeny; Turgor; turgor pressure; turgor‐driven growth; turgor‐time; Water availability
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.13989

The process of leaf elongation in grasses is characterized by the creation and transformation of distinct cell zones. The prevailing turgor pressure within these cells is one of the key drivers for the rate at which these cells divide, expand and differentiate, processes that are heavily impacted by drought stress. In this article, a turgor‐driven growth model for grass leaf elongation is presented, which combines mechanistic growth from the basis of turgor pressure with the ontogeny of the leaf. Drought‐induced reductions in leaf turgor pressure result in a simultaneous inhibition of both cell expansion and differentiation, lowering elongation rate but increasing elongation duration due to the slower transitioning of cells from the dividing and elongating zone to mature cells. Leaf elongation is, therefore, governed by the magnitude of, and time spent under, growth‐enabling turgor pressure, a metric which we introduce as turgor‐time. Turgor‐time is able to normalize growth patterns in terms of varying water availability, similar to how thermal time is used to do so under varying temperatures. Moreover, additional inclusion of temperature dependencies within our model pioneers a novel concept enabling the general expression of growth regardless of water availability or temperature. A model for grass leaf elongation is presented, which combines mechanistic growth based on turgor pressure and leaf ontogeny. An inverse relation was found between the rate and duration of the elongation rate, allowing for uniform expression of growth in terms of a new concept called ‘turgor‐time’.