The reduction in leaf area precedes that in photosynthesis under potassium deficiency: the importance of leaf anatomy

Abstract

Summary Synergistic improvement in leaf photosynthetic area and rate is essential for enhancing crop yield. However, reduction in leaf area occurs earlier than that in the photosynthetic rate under potassium (K) deficiency stress. The photosynthetic capacity and anatomical characteristics of oilseed rape (Brassica napus) leaves in different growth stages under different K levels were observed to clarify the mechanism regulating this process. Increased mesophyll cell size and palisade tissue thickness, in K‐deficient leaves triggered significant enlargement of mesophyll cell area per transverse section width (S/W), in turn inhibiting leaf expansion. However, there was only a minor difference in chloroplast morphology, likely because of K redistribution from vacuole to chloroplast. As K stress increased, decreased mesophyll surface exposed to intercellular space and chloroplast density induced longer distances between neighbouring chloroplasts (Dchl‐chl) and decreased the chloroplast surface area exposed to intercellular space (Sc/S); conversely this induced a greater limitation imposed by the cytosol on CO2 transport, further reducing the photosynthetic rate. Changes in S/W associated with mesophyll cell morphology occurred earlier than changes in Sc/S and Dchl‐chl, inducing a decrease in leaf area before photosynthetic rate reduction. Adequate K nutrition simultaneously increases photosynthetic area and rate, thus enhancing crop yield.

Leaf Phenological Stages of Winter Oilseed Rape (Brassica napus L.) Have Conserved Photosynthetic Efficiencies but Contrasted Intrinsic Water Use Efficiencies at High Light Intensities

“…Thus, a longer path within a liquid phase for CO 2 should affect its diffusion to the chloroplast. Recent studies reported that mesophyll conductance was strongly limited by the cytoplasm in mature leaves of oilseed rape compared to young leaves and significantly contributed to the limitation of net CO 2 assimilation (Lu et al, 2019;Hu et al, 2020). Therefore, the increase of stomatal aperture in FIGURE 6 | Proposed model for the regulation of intrinsic water use efficiency (iWUE) by senescence in winter oilseed rape leaves at high light intensities.…”

“…Therefore, the increase of stomatal aperture in FIGURE 6 | Proposed model for the regulation of intrinsic water use efficiency (iWUE) by senescence in winter oilseed rape leaves at high light intensities. Leaf senescence in winter oilseed rape leads to an increase of the vacuolar volume of cells of the palisade parenchyma, which can limit photosynthesis by decreasing mesophyll conductance of CO 2 (Musse et al, 2013;Sorin et al, 2015;Lu et al, 2019;Hu et al, 2020). In this model, senescent leaves of oilseed rape increase their stomatal aperture compared to young/mature leaves to increase the diffusion of CO 2 toward chloroplasts for photosynthesis.…”

Comparative Proteomics of Mulberry Leaves at Different Developmental Stages Identify Novel Proteins Function Related to Photosynthesis

“…A previous work has reported the ultrastructure (e.g., leaf thickness, cell densities, cell size etc.) to vary between new born and mature leaves in several angiosperms (Proietti et al, 2000;Hu et al, 2020). The PI ABS value is another important indicator of PSII photochemical activity.…”

“…The net photosynthesis rate is relatively low in young and unexpanded leaves and peaks at approximately fullleaf expansion, where it remains stable and subsequently declines (Wilson and Cooper, 1969;Xie and Luo, 2003;Reddy et al, 2017;Gara et al, 2018;Durgadevi and Vijayalakshmi, 2020). The development stage of leaves varies with their positions, therefore different leaf structures (Hu et al, 2020), exhibiting distinct mesophyll cell numbers and chloroplasts per leaf area, resulting in various photosynthetic capacities (Araus et al, 1997;Hu et al, 2020). In addition, leaf position also affects light availability.…”

Reduced mesophyll conductance by cell wall thickening and chloroplasts decreasing driven the decline of photosynthesis under sole NH4+ supply

“…In particular, liquid-phase limitation accounts for more than 80% of the total limitation, in which the cell wall thickness (T cw ) and chloroplast surface area exposed to intercellular airspace per unit leaf area (S c /S) are the two dominating components that affect g m (Flexas et al, 2021). There are ample studies showing a significant positive correlation between S c /S and g m , and the S c /S was considered the uppermost parameter in determining g m (Hu et al, 2020;Tomás et al, 2013). While the cell wall is often negligible, because it accounts for a tiny fraction of the CO 2 diffusion length (Carriquí et al, 2020), has a comparative larger pore size and variability , and quite a static influence on photosynthesis (Evans et al, 2009).…”