Abstract
BackgroundUnder high plant density, intensifying competition among individual plants led to overconsumption of energy and nutrients and resulted in an almost dark condition in the lower strata of the canopy, which suppressed the photosynthetic potential of the shaded leaves. Leaf removal could help to ameliorate this problem and increase crop yields. To reveal the mechanism of leaf removal in maize, tandem mass tags label-based quantitative analysis coupled with liquid chromatography–tandem mass spectrometry were used to capture the differential protein expression profiles of maize subjected to the removal of the two uppermost leaves (S2), the four uppermost leaves (S4), and with no leaf removal as control (S0).ResultsExcising leaves strengthened the light transmission rate of the canopy and increased the content of malondialdehyde, whereas decreased the activities of superoxide dismutase and peroxidase. Two leaves removal increased the photosynthetic capacity of ear leaves and the grain yield significantly, whereas S4 decreased the yield markedly. Besides, 239 up-accumulated proteins and 99 down-accumulated proteins were identified between S2 and S0, which were strongly enriched into 30 and 23 functional groups; 71 increased proteins and 42 decreased proteins were identified between S4 and S0, which were strongly enriched into 22 and 23 functional groups, for increased and decreased proteins, respectively.ConclusionsDifferent defoliation levels had contrastive effects on maize. The canopy light transmission rate was strengthened and proteins related to photosynthetic electron-transfer reaction were up-regulated significantly for treatment S2, which improved the leaf photosynthetic capacity, and obtained a higher grain yield consequently. In contrast, S4 decreased the grain yield and increased the expressions of proteins and genes associated with fatty acid metabolism. Besides, both S2 and S4 exaggerated the defensive response of maize in physiological and proteomic level. Although further studies are required, the results in our study provide new insights to the further improvement in maize grain yield by leaf removal.
Highlights
Under high plant density, intensifying competition among individual plants led to overconsumption of energy and nutrients and resulted in an almost dark condition in the lower strata of the canopy, which suppressed the photosynthetic potential of the shaded leaves
We identified a series of proteins involved with this process, including chlorophyll a-b binding proteins (CABs; A0A096RF43, A0A096RM67, A0A096UJK9, A0A096S5Z5, B4FV94, B4FXB0, B6SZT9, B6T892, K7TXI5, and Q41746), photosystem II (PSII) reaction centre protein (P05641, P24993, and P48187), oxygen-evolving enhancer protein (A0A096U686), cytochrome oxidase (A0A096U038 and K7UZJ0), cytochrome (A0A096Q1T0 and B6UBZ9), plastocyanin (B6SSB9), photosystem I (PSI) assembly protein (A0A096TR75), PSI reaction centre subunit (B4G1K9), ferredoxin (B6TVC7), ATP synthase (K7VI25, K7VN08, P00835, P17344, and P48186) and F1F0-ATPase inhibitor protein (B6T5U0)
Based on our study, we demonstrated that different defoliation levels had contrastive effects on maize
Summary
Under high plant density, intensifying competition among individual plants led to overconsumption of energy and nutrients and resulted in an almost dark condition in the lower strata of the canopy, which suppressed the photosynthetic potential of the shaded leaves. When plants are injured after artificial defoliation, eaten by animals or pests, the leaf area decrease thereafter [13, 14], residual organs have a compensating effect when the photosynthetic organs injured above a certain threshold level [15, 16]. Removing the uppermost two or four leaves in maize appeared to stimulate an increase in net photosynthetic rate (Pn), stomatal conductance, and Chl content of the ear leaf. The photosynthesis extent of leaves during grain filling can be affected by canopy structure [20] and the corresponding variations in light conditions may lead to changes in the expression levels of proteins, which invariably leads to changes in plant metabolism [21]
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