Basal axillary buds in pea are hydraulically connected to the stem but are protected during drought by osmotic adjustment.

Plants prioritise water allocation to tissues that support their survival and reproduction during drought, but little is known about their tissue-specific drought tolerance mechanisms. In the case of basal buds, the extent to which they are hydraulically connected to the stem is unclear, as are their drought resistance mechanisms. To address these questions in the herbaceous annual Pisum sativum L. (cv. Torsdag), we used optical dendrometry to monitor the expansion and contraction of basal buds and their adjacent stems during their diurnal cycle and longer-term during drought. We also measured water potential and osmotic potential of buds and stems. Dimensions of buds and stems oscillated synchronously throughout their diurnal cycle, indicating a functional hydraulic connection. Buds maintained turgor during drought by osmotic adjustment (OA) to maintain a pressure differential with the main plant xylem. Thus, immediate outgrowth of buds occurred upon rewatering. We conclude that OA protects buds during drought, allowing them to retain water and viability. This strategy enables growth and flowering of lateral branches postdrought, even if the primary shoot is damaged. We expect this mechanism to play a significant role in a wide range of annuals during drought, including many crop species.