Date Published: July 21, 2017
Publisher: Public Library of Science
Author(s): Dan Feng, Yanwei Wang, Tiegang Lu, Zhiguo Zhang, Xiao Han, Min Zhao.
Plant leaves exhibit differentiated patterns of photosynthesis rates under diurnal light regulation. Maize leaves show a single-peak pattern without photoinhibition at midday when the light intensity is maximized. This mechanism contributes to highly efficient photosynthesis in maize leaves. To understand the molecular basis of this process, an isobaric tag for relative and absolute quantitation (iTRAQ)-based proteomics analysis was performed to reveal the dynamic pattern of proteins related to photosynthetic reactions. Steady, single-peak and double-peak protein expression patterns were discovered in maize leaves, and antenna proteins in these leaves displayed a steady pattern. In contrast, the photosystem, carbon fixation and citrate pathways were highly controlled by diurnal light intensity. Most enzymes in the limiting steps of these pathways were major sites of regulation. Thus, maize leaves optimize photosynthesis and carbon fixation outside of light harvesting to adapt to the changes in diurnal light intensity at the protein level.
Photosynthesis is the most important process for generating energy and supplying organic materials to plants. During this process, light energy is converted to chemical energy, and carbon from CO2 is incorporated into organic molecules in plant leaves. These processes support nearly all living organisms on Earth . In diurnal cycling regulation, light intensity is the most important environmental factor impacting the photosynthesis rate [2–4]. Plant leaves have developed mechanisms to adapt to variations in light intensity caused by environmental conditions [5–7]. Over a certain range, the photosynthesis rate is positively correlated with light intensity [8–10]. Once the photosynthetic rate is maximized, plants cannot adapt to increased light intensity, and thus, the rate can decrease because of light damage under strong intensity illumination [11, 12]. To improve crop production, research has focused on photosynthesis as the basic production process of bioenergy and organic materials . Studies of various crops have revealed different patterns of photosynthesis rates that are dependent on the pattern of light intensity during the diurnal cycle [11, 14]. In general, the diurnal patterns of the photosynthetic rate in crops can be classified into two categories: a single-peaked curve, such as in Zea mays [15, 16] and Sorghum bicolor, and a double-peaked curve, such as Oryza sativa. Some crops, such as Glycine max, exhibit different diurnal patterns among different cultivars. Maize, in which the photosynthetic rate shows a single-peaked curve, can endure high-intensity light at midday, and the diurnal pattern of its photosynthetic rate matches the curve of diurnal light intensity with a slight delay. Rice , which has a double-peaked curve, suffers from photoinhibition at midday, when high light intensity causes stomata closure and low efficiency in the chloroplasts. Hence, maize has a higher photosynthetic rate than rice [1, 18–21]. Consequently, it is widely accepted that efficient photosynthesis in maize leaves contributes to this plant’s high productivity [22, 23]. To understand the molecular mechanism involved in the diurnal regulation of the photosynthetic rate in maize, several studies have been conducted on gene regulation, photosynthetic enzyme activity and photosynthate partitioning [24–26]. The results revealed that the diurnal regulation of the photosynthetic rate requires delicate control of the genetic composition, gene expression, protein levels, protein modification and metabolic transport related to photosynthesis .
Leaves are the key organ in plants in which photosynthesis occurs, which supplies energy and carbon materials. One important regulatory mechanism of photosynthesis is the control of enzyme protein levels. During a diurnal cycle with varying light intensity, leaves optimize their photosynthesis rates to adapt to the environment by adjusting enzyme levels .
The raw data accompanying this study have been deposited in iProX with the identifier IPX00085001.