Growth and survival strategies of oilseed rape (Brassica napus L.) leaves under potassium deficiency stress: trade-offs in potassium ion distribution between vacuoles and chloroplasts.

Potassium (K) is a prevalent limiting factor in terrestrial ecosystems, with approximately one-eighth of the world's soils undergoing K+ deficiency stress. Upon encountering K+ deficiency stress, leaf area (LA) declines before the net photosynthetic rate (An). The sequential alterations fundamentally represent the adaptive trade-off between survival and growth in plants subjected to K+ deficiency stress. This trade-off is hypothesized to be linked to the differences in the subcellular distribution of limited K+ resources. Thus, the K+ distribution and apparent concentration in subcellular compartments, along with the LA and An characteristics of rapeseed leaves at various developmental stages and K+ supply conditions were quantified to elucidate the mechanisms by which subcellular K+ regulates leaf growth and survival. The results revealed that during the early stages of K+ deficiency, leaves actively downregulate growth to sustain normal physiological functions. This is primarily accomplished by lowering the K+ distribution and apparent concentration in vacuoles, restricting LA expansion, and enhancing K+ distribution to chloroplasts to ensure An. Prolonged K+ deficiency decreased the apparent K+ concentration in chloroplasts below the critical threshold (37.8 mm), disrupting chloroplast structure and function, impairing An, and ultimately threatening the survival of rapeseed. Hence, sustaining an adequate concentration of K+ within chloroplasts is crucial for preserving leaf photosynthetic efficiency and ensuring survival under K+ deficiency stress. In conclusion, under K+ deficiency stress, leaves regulate LA and An by trade-offs in the K+ distribution between vacuoles and chloroplasts to coordinate growth and survival.