Susan S. Han

Role of ethylene in postharvest quality of cut oriental lily ‘Stargazer’

The effects of endogenous and exogenous C2H4 and C2H4 inhibitors on the postharvest leaf and flower quality of Oriental lily ‘Stargazer’ were investigated. Endogenous C2H4 was not produced by freshly harvested excised leaves or flowers. Treatment of freshly harvested excised flowers, buds, leaves, and intact cut stems with C2H4 concentrations as high as 10 µl·l−1 did not affect bud opening or longevity or the development of leaf yellowing. Therefore, treatment with anti-C2H4 compounds, such as silver thiosulfate (STS) and 1-methylcyclopropene (1-MCP), did not improve the quality of the flowers. Data thus indicate that freshly harvested ‘Stargazer’ were not sensitive to C2H4. Sensitivity of ‘Stargazer’ to C2H4, however, increased dramatically following cold storage, as exposure of cold-stored stems to C2H4 concentrations as low as 0.3 µl·l−1 significantly affected bud opening. The development of leaf yellowing on cold-stored stems was not affected by the exogenous C2H4. Pretreating cold-stored stems with 1-MCP significantly reduced blasting of small buds that failed to develop due to carbohydrate depletion and reduced the percentage of buds that did not fully open. Concurrently, 1-MCP did not affect the quality of the leaves. These data indicate that sensitivity of cut lilies to C2H4 differs following cold storage and that 1-MCP is a more suitable anti-C2H4 compound than STS. Furthermore, studies on endogenous C2H4 production revealed that, while C2H4 was not detected in freshly harvested buds and leaves, it was produced by both following cold storage. The latter produced C2H4 at a higher rate than the former. Results of this study clearly indicate that there are two situations in which lilies will benefit from pretreatment with an anti-C2H4 compound (1) when cut stems contain buds that are marginally small for opening and (2) when cut stems will be cold stored before marketing.

Respiratory and carbohydrate changes during ethylene-mediated flower induction in Dutch iris

Abstract The promotion of flowering in small Dutch iris (Iris × hollandica Hoog., cv. ‘Ideal’) bulbs by treatment for 24 h with 10 μl l−1 ethylene was associated with enhanced respiration, which continued long after the end of ethylene treatment. Shorter ethylene treatments, which were partially effective in inducing flowering, resulted in lower and shorter bursts of respiration. Changes in the soluble carbohydrate contents of the ethylene-treated bulbs were not detected until following the cold treatment. The possible mechanisms by which ethylene stimulates flowering are discussed.

Morphology of flower initiation of brodiaea

The main axis of dormant brodiaea corms (Triteleia laxa) harvested from the field in the summer comprises a leaf sheath, two leaf primordia, and a vegetative meristem. Floral induction, as indicated by initiation of bracts on the flanks of the apical meristem, occurs after corm dormancy is broken. The bracts enlarge and enclose the reproductive dome, which then divides to form floral primordia of different ages. The daughter corm, which forms from the basal portion of the stem, starts to enlarge early in the growing season. Unlike many other geophytes, there is little competition, in brodiaea, for assimilates between the vegetative propagules (daughter corm and cormels) and the developing inflorescence.

Developmental Events Associated with the Critical Stage for Sex Determination in Wild‐Rice Florets

The developmental events of florets and a critical stage for sex determination in two wild‐rice populations (Zizania palustris cv. Franklin and Zizania palustris cv. K‐2Pi) have been identified. Formation of bisexual florets precedes the development of both male and female florets. Developmental indicators, established by measuring the length of florets and panicles, indicate that the critical stage for sex determination occurs when floret and panicle lengths are 1–2 mm and 3 cm, respectively. The stage of floret development at which sex determination occurs is the same in the two investigated wild‐rice populations. Organ suppression in bisexual florets is an essential step for sex determination during the formation of unisexual florets. Histological examination of suppressed stamens or pistils in unisexual florets of wild‐rice indicates that cell death does not occur during sex determination. In addition, the length of anthers and pistils in bisexual florets indicates that floral development in the transition zone is normal when compared with the male florets in the male spikelets and female florets in the female spikelets.