Dr. Maryam Shahbazi received her PhD in Molecular Plant Physiology from Grenoble I (Joseph Fourier) University- France in 2008. She is currently working as a Research Assist Professor and project leader in Agricultural Biotechnology Research Institute of Iran (ABRII). She is in charge of Education and Training Office of ABRII. She is also an invited lecturer of Tehran University. She has supervised more than 20 graduated students. Maryam conducted physiological researches on traits and mechanisms contributing to crop stress tolerance including drought and salinity, and her research focused on gene discovery in crop plants. Also, she is a molecular physiologist in the field of photosynthesis, photosynthetic electron transport particularly in the redox status of the plastoquinone pool which is very responsive and important in plants when exposing to stress conditions.
The effects of graduated drought stress on gas exchange, the regulation of photosynthetic electron transport and the role of plastid terminal oxidase (PTOX) were studied in cultivated barley and its drought tolerant wild relative. PTOX has an indispensable and direct role in photosynthesis, namely its influence on the redox status of the plastoquinone pool between PSII and PSI probably via chlororespiratory mechanism. In order to study of the effects of mild and severe drought stress on photosynthesis in barley in response to drought stress, an experiment was conducted on tolerant (Yousof), susceptible (Morocco) cultivars and an Iranian tolerant wild barley genotype (Spontaneum). Drought treatment started in two-leaf stage via withholding water (30% and 10% water holding capacity of soil, mild and severe drought stress, respectively) compared to well-watered condition. Drought stress significantly affected plant water status and caused decrease in relative water content as well as increase in water and osmotic potential and led to increase in leaf temperature. Under drought stress an increase in hydrogen peroxide accompanied with increase in malondialdehyde content and electron leakage, especially in Morocco cultivar, was observed. Antioxidant systems including enzymatic (catalaze, ascorbate peroxidase and peroxidase) and non enzymatic (α-tocopherol, total ascorbate, reduced ascorbate) increased during drought treatment especially in Yousof and Spontaneum. In addition, drought stress led to change in photosynthetic pigments profile where amounts of chlorophyll a and b decreased under drought stress. Fast chlorophyll a fluorescence kinetics (OJIP-test) including minimal fluorescence, rate of active reaction centers, efficiency of water splitting complex, yield of primary photochemistry and electron transport, yield of thermal dissipation, quantum yield of photosystem II as well as performance index were also negatively affected by drought stress. These changes were more prominent in Morocco cultivar. Similarly, chlorophyll a transient curve of Morroco cultivar under drought stress, exhibited a considerable increase in fluorescence intensity at phases O, J, I and P compared to other cultivars. The ptox transcript and the PTOX protein levels were exclusively increased in Spontaneum under severe drought stress. As well, exposure of barley plants to nPG, PTOX inhibitor, revealed that in Spontaneum, redox state of plastoquinon pool notably relies on function of PTOX and this protein plays a key role in keeping plastoquinone pool oxidize during severe drought stress. Consistent to achieved findings, gene expression and protein content of PTOX did not exhibited significant changes in Yousof and Morocco cultivar under drought stress. We conclude that in cultivated barley and Spontaneum plants highly differentially respond to drought stress, and in drought-stressed Spontaneum, plastid terminal oxidase acts as an alternative electron sink.