Manipulating stomatal density affects plant growth, yield and drought tolerance

Photosynthesis in leaves is dependent on CO2 reaching mesophyll cells which contain the bulk of chlorophyll, yet most of the leaf is enveloped by a waxy cuticle which is almost impermeable to CO2 and water. Gas exchange is enabled through pores on the leaf epidermis called stomata which are each formed by two specialised guard cells morphologically distinct from general epidermal cells and able to react to their environment by increasing or decreasing cell turgor. This enables the stomatal pores to open or close depending on the plant’s need to acquire CO2 or conserve water, allowing much needed flexibility in plant water relations. The experiments detailed in this thesis have the broad aim of determining correlations between altered stomatal density, stomatal size, leaf gas exchange, drought tolerance, and plant water use efficiency. Most experiments have been carried out on a set of Arabidopsis mutants with altered expression of Epidermal Patterning Factors (EPFs), a peptide family which is involved in the development of stomatal patterning and density on the leaf. Chapter 3 addresses the question of how altering the EPF family of peptides affects leaf morphology and more specifically whether stomatal densities correlate with stomatal size in Arabidopsis plants with altered EPF expression patterns. Chapter 4 examines the leaf gas exchange properties of Arabidopsis and questions whether or not altering stomatal density impacts leaf water use efficiency and photosynthesis. Finally, experiments in chapter 5 highlight how combined changes to leaf morphology and gas exchange due to altered EPF expression impact drought tolerance, seed yield and rosette morphology. Although most of this work was carried out on Arabidopsis plants, stomatal densities and water use efficiencies were also examined in a set of Barley cultivars to determine whether similar trends could be observed in a directly agriculturally useful plant. Results of these experiments and suggested directions to pursue this work in barley are summarised in chapter 6.