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

SUMMARY 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 m m ), 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.