Formation of new networks of earlywood vessels in seedlings of the deciduous ring-porous hardwood Quercus serrata in springtime

Abstract

Complete differentiation of the first earlywood vessels occurred earlier in upper regions of stems than in middle and lower regions when buds swelling in a ring-porous hardwood Quercus serrata seedlings. In deciduous ring-porous hardwoods, the timing of the onset of conduction of water via the networks of the current year’s earlywood vessels is very important for the growth of buds and shoots because the main pathways for conduction of water are the networks of the current year’s earlywood vessels. The purpose of this study was to visualize the formation of the networks of first earlywood vessels in the current year’s xylem of seedlings of the deciduous ring-porous hardwood Quercus serrata. We monitored the distribution of water in the current and the previous year’s secondary xylem at the cellular level in upper, middle and lower regions of stems during the formation of earlywood vessels by cryo-scanning electron microscopy after freeze-etching. We also examined how changes in water distribution were correlated with leaf phenology. The contents of the first vessel elements in the upper region of the stem changed from cytoplasm-rich to water earlier than those in middle and lower regions of the stem when buds were increasing in size. At bud break, vessel elements were filled with water throughout the entire stem. When the cambium was dormant and during formation of earlywood vessels, the previous year’s latewood vessels were filled with water. Our results showed that complete differentiation of vessel elements occurred earlier in upper regions of stems than in middle and lower regions. Moreover, the functional networks of the previous year’s latewood vessels appeared to be involved in supplying water to new networks of earlywood vessels in the current year’s xylem.