Greening Rates and Photosynthetic Development of Etiolated Leaves in Four Crop Species

Abstract

Many aspects of early plant development are dependent on light exposure, but functional measures of chlorophyll development and chlorophyll fluorescence have not been conducted during a dark-to-light transition in seedlings. To study chlorophyll biosynthesis and overall photosynthetic activity development in leaves, seeds were germinated in darkness and etiolated leaves were then allowed to develop in lighted conditions. Zea mays (corn), Sorghum bicolor (sorghum), Vicia faba (broad bean), and Triticum aestivum (wheat) were investigated for the first eight days of sunlight exposure. Chlorophyll content and chlorophyll fluorescence measurements were conducted daily on the first true leaf on each plant. The first 5 days of the experiment, days 0 to 4 in light, had the greatest physiological impact on leaves of etiolated plants as they transitioned to a green state. Vicia faba and T. aestivum plants developed more chlorophyll and had faster rates of chlorophyll accumulation compared to Z. mays and S. bicolor plants. The majority of chlorophyll fluorescence parameters measured had less than a 20 percent change from days 4 to 8 in light. Chlorophyll fluorescence parameters in V. faba and Z. mays were higher than in T. aestivum and S. bicolor and took longer to reach a maximum value. Chlorophyll content and chlorophyll fluorescence had similar patterns of development, with consistent differences among species. This indicates that development of photosynthetic electron transport is related to chlorophyll content and likely differs based on leaf structure or other physiological factors.