The control of stomatal properties in rice (Oryza sativa L.) and their influence on photosynthetic performance

The earliest stages of leaf development in rice occur without direct exposure to the prevailing light environment, yet the mature leaf shows a number of morphological and physiological adaptations to light. Systemic signals generated in mature leaves are thought to play an important role in controlling the response of the young leaf primordia, but the precise developmental window during which this response can occur requires further characterisation. Stomatal size, density and distribution are likely to be key elements of this response since they play an important role in controlling gas exchange in the mature leaf, yet the cell division processes that control stomata formation are limited to relatively early stages of leaf development. The work reported here describes the process of stomata formation during rice leaf development and, in particular, identifies the stages up to and including the P3 stage as the phase during which the stomatal differentiation and patterning system is responsive to a shift of the plant from high to low irradiance. Careful staging of the transfer revealed that various aspects of stomatal size could be altered during this early phase of rice leaf development. Variable guard cell width (linked to variation in epidermal cell file width in the rice leaf) was identified as a key variable in this morphological response. Physiological analysis of mature leaves with altered stomatal properties revealed the extent to which biochemical/physiology adaptations could compensate for altered potential parameters of gas exchange. Finally, a whole-mount in situ hybridisation (WISH) procedure was optimized and proven to work in a reliable fashion using probes for various genes, thus providing a new tool for the visualisation of gene expression in rice leaves. This paves the way for the analysis of gene expression during the very early stages of leaf development when stomatal differentiation occurs. The work advances our understanding of the control of stomatal formation in rice and its potential influence on leaf photosynthetic performance. The method developed for the analysis of gene expression will enable future work to characterise the genetic mechanism underlying the environmental control of stomatal properties