Resumen:
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.