Abstract
To gain more insight into the physiological function of shade and how shade affects leaf size, we investigated the growth, leaf anatomical structure, hormones and genes expressions in soybean. Soybean seeds were sown in plastic pots and were allowed to germinate and grow for 30 days under shade or full sunlight conditions. Shade treated plants showed significantly increase on stem length and petiole length, and decrease on stem diameters, shoot biomass and its partition to leaf also were significantly lower than that in full sunlight. Smaller and thinner on shade treated leaves than corresponding leaves on full sunlight plants. The decreased leaf size caused by shade was largely attributable to cell proliferation in young leaves and both cell proliferation and enlargement in old leaves. Shade induced the expression of a set of genes related to cell proliferation and/or enlargement, but depended on the developmental stage of leaf. Shade significantly increased the auxin and gibberellin content, and significantly decreased the cytokinin content in young, middle and old leaves. Taken together, these results indicated that shade inhibited leaf size by controlling cell proliferation and enlargement, auxin, gibberellin and cytokinin may play important roles in this process.
Highlights
Intercropping is practiced widely by smallholder farmers across the world[1, 2]
Cell division occurs and generates new cells, the size of cells remains relatively constant and small, when cell division is finished, leaf growth is largely depends on cell expansion, which will result in an enlargement in cell size[18]
It has been reported that cell expansion is more important than cell division in leaf growth under low photosynthetically active radiation conditions[17], but other study pointed that cell number, not cell size, contributes to the reduced leaf size of plants grown in low R/FR relative to high R/FR24
Summary
Intercropping is practiced widely by smallholder farmers across the world[1, 2]. But shade environment by taller crops usually limited the growth of shorter crops in intercropping[3, 4]. It has been reported that cell expansion is more important than cell division in leaf growth under low photosynthetically active radiation conditions[17], but other study pointed that cell number, not cell size, contributes to the reduced leaf size of plants grown in low R/FR relative to high R/FR24. We have found that soybean leaves became smaller when they grown under shade condition in intercropping systems, and plant hormones might be involved in inhibition on leaf size under shade as suggested by transcriptome analysis[8, 28]. It remains uncertain how shade effect the leaflet size of trifoliate in soybean. To gain more understanding of the effects of shade on leaf size, the objectives of this study were: 1) to investigate the morphology and cellular mechanisms of leaf growth regulated by shade in soybean. 2) to quantify the expression levels of twenty genes related to cell proliferation and/or cell enlargement in response to shade. 3) to determine the variations of auxin, cytokinin, gibberellin and brassinolide contents
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