Environmental and developmental regulation of carotenoid metabolism in Arabidopsis leaves

Abstract

The regulation of carotenogenesis during the leaf maturation, before the onset of senescence, remains poorly explored. In this thesis, I demonstrated that young leaves of Arabidopsis, which have a high chloroplast density because of the high density of actively dividing and expanding mesophyll cells, can accumulate nearly 60 % higher amounts of both carotenoids and chlorophylls compared to the older leaves. Analysis of a range of mutants and gene overexpression genotypes revealed that age-related decline in carotenoids in older leaves was not associated with biosynthesis or degradation pathways of carotenoids neither with the developmental phase identities of leaves. I also discovered younger leaves were highly plastic in decreasing the level of both carotenoids and chlorophylls rapidly in response to short-term (24-hours) exposure to darkness, low temperature (7 oC), and norflurazon (a bleaching herbicide) treatment while the elevated level of atmospheric CO2 increased the level of both pigments in younger leaves. The level of carotenoids and chlorophylls was unaffected in older leaves regardless of the perpetual increase in atmospheric CO2 and short-term environmental and norflurazon treatments. Pigment accumulation in younger leaves demonstrated rapid responsiveness to environmental conditions and norflurazon, arguably, due to the higher rate of plastid biogenesis and division in the rapidly dividing and expanding cells. Collectively, the state of chloroplast development and chloroplast density can be the primary determinants of the photosynthetic pigment content in leaves. Young leaves, thus, can provide better in-planta model systems to decipher how developmental and environmental signals affect plastid development, signalling, and carotenoid biosynthesis during Arabidopsis leaf development.

Date of Award	2018
Original language	English