Mechanical Aspects of Rapid Flower Opening in Asiatic Lily

Several processes contribute to the rapid opening of Asiaticlily flowers. Opening occurs after the tepals stop increasingin length, and have reached maximum thickness. Up to day -0.5(where day 0 is time that flowers are half-open), the sepalsentirely encase the petals, and their edges are tightly claspedin deep grooves beside the petal midribs. At day -0.5 to -0.3,the petal midrib reduces in width, opening the groove and allowingthe tepals to pull apart (bud ‘cracking’). Unlockingis not complete until about day -0.15: it is not the key eventdirecting opening, but helps to sharpen its onset. The midribscontrol subsequent opening, pulling the laminae behind them.In the first 3–4 h of opening (‘dark phase’),the main process is an increase in the angles the midribs makewhere they join the pedicels. During this time, the petals andsepals are only slightly curved. Subsequently through to day0.5 (the ‘light phase’), an increasingly markedcurvature of the midribs pulls the tepals further apart andcauses them to progressively reflex. By day 1 the flowers aremature and the laminae are no longer being pulled by the midribs.In studies of isolated tissue segments, we found that in thelater stages of opening there is greater cell expansion in theepidermis of the inner surfaces, contributing to the recurving.Petal expansion is accompanied by cell separation and osmoticchanges, and inhibitors of starch hydrolysis inhibit expansionof petal segments. Of the various processes operating duringlily opening, we believe that the most influential is the changein angle between midribs and pedicel, suggesting a pulvinus-likemechanism.Copyright 2000 Annals of Botany Company Flower opening, lily, mechanics, petal lock, osmotic changes, starch, epinasty