Photosynthetic and respiratory characterization in vascular and crop plant species: from an evolutionary perspective to a sustainable agriculture.

Abstract

The physical and chemical properties of the terrestrial environment were important for plant land colonization and later diversification, promoting physiological, morphological, and metabolic adaptations to deal with changes in energy input, gravity, and humidity. From a primitive thalloid-like shape, the photosynthetic organ evolved into the appearance of a large variety of leaf forms and stomata allowing increases of the efficiency of water transport and thermoregulation for the benefit of plant gas exchange. Besides, the replacement of an inefficient rudimentary rhizoid system in water and nutrient absorption, by an early symbiosis with soil microorganisms, allowed plant roots to adapt to poor nutrient soils. Along with these aboveground and belowground adaptations, the progressive evolution of an aerobic cell metabolism, involving oxygen consumption in mitochondria, increased both the efficiency of oxidative phosphorylation and energy homeostasis for the benefit of plant carbon metabolism. In the present thesis, I studied the relationship between energy homeostasis and carbon metabolism in plants along three chapters that explore different scenarios of plant adaptations to terrestrial environments: (1) In chapter one, this relationship is explored through comparisons between terrestrial and palustrine plants. (2) In the second chapter, this relationship is studied during drought by exploring the importance of leaf shape for both photosynthetic capacity and energy dissipation as convective heat. (3) Finally, in the third chapter, this relationship is analyzed by reviewing the role of root respiration during symbiosis with soil microorganisms. From photosynthetic and respiratory characterizations in vascular plants and crop species, the results of this thesis suggest that: (1) terrestrial plants display higher rates of photosynthesis and redox balance because they are exposed to higher reducing conditions in their environments; (2) leaf shape controls the energy input by a physical mechanism that benefit carbon assimilation and optimal temperature range; (3) root respiration may regulate the energy balance in plants under nutrient deficiency and during symbioses with soil microorganisms. Overall, these results contribute to understand the coordination between several biochemical and physiological mechanisms important for energy assimilation and later conversion into carbon compounds and plant growth, being of interest for agricultural improvement and community development programs.