Growth and survival strategies of oilseed rape (<i>Brassica napus</i> 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 (A_n). 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 A_n 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 A_n. Prolonged K⁺ deficiency decreased the apparent K⁺ concentration in chloroplasts below the critical threshold (37.8 mm), disrupting chloroplast structure and function, impairing A_n, 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 A_n by trade-offs in the K⁺ distribution between vacuoles and chloroplasts to coordinate growth and survival.