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Stem elongation and leaf orientation in Lilium longiflorum Thunb. were influenced more by the difference (DIF) between day temperature (DT) and night temperature (NT) than absolute DT or NT from 14 to 30 C. Plant height and internode length increased 129 and 382%, respectively, as DIF (DT‐NT) increased from –16 to 16 C as compared to only 15 and 58% when either DT or NT was increased from 14 to 30 C, respectively. Leaf orientation, defined as the angle between a line perpendicular to the stem and the line from the leaf base to the leaf tip, increased 43° (leaves became more upright) as DIF increased from –16 to 16 C. In contrast to plant height, internode length, and leaf orientation, leaf and flower length were influenced more by absolute temperature than DIF. Leaf and flower length decreased 32 and 14%, respectively, as NT increased from 14 to 30 C. DT had little effect on either leaf or flower length. The influence of DIF on stem elongation suggested that thermomorphogenesis was not a function of total plant carbohydrate or carbohydrate translocation. Instead, DIF appeared to influence the endogenous gibberellin content or the response of plant tissue to gibberellin. Similarities between thermomorphogenic plant responses and photomorphogenic plant responses suggested that these two processes may be related with respect to their perception and/or transduction.

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correlated with the difference between DT and NT (DIF) rather than the actual DT/NT under which plants are grown when temperatures range from 10 to 26C (Erwin, 1991; Erwin et al., 1989b; Moe and Heins, 1990; Moe et al.,

A system to study the basis of high temperature-induced floral bud abortion using naturally occurring variation for heat-tolerance of floral development among Arabidopsis thaliana (L.) Heynh. wild-collected accessions is described. High temperature-induced floral bud abortion was dependent on both temperature and duration of exposure. Exposing the inflorescence alone to high temperature was sufficient to induce floral bud abortion, and Col-0 and No-0 photosynthetic rates were similar during high temperature exposure and recovery, indicating that high temperature induced floral abortion is not simply due to reductions in carbon assimilation under high temperatures. Determining that exposing floral buds alone to high temperature is sufficient to induce abortion and identifying the stages of floral development sensitive to high temperature-induced abortion will aid in identifying the developmental events subject to disruption under high temperatures.

Genetic modification and manipulation offers the possibility of introducing novel traits into existing plants, thereby increasing marketability. Polyploid induction has in the past produced plants that are more compact and have larger flowers, leaves, and fruit, making them more desirable to consumers. The effect of pulse treatments (0, 24, 48, and 72 h) of colchicine (25, 50, 125, and 250 μm) or oryzalin (30, 60, 90, and 120 μm) on in vitro-grown Watsonia lepida N.E. Brown shoots was investigated. Explant survival was higher and more consistent with oryzalin treatment compared with treatment with colchicine. More mixoploids than tetraploids were produced with both compounds. The optimum treatment for producing tetraploids was 120 μm oryzalin for 24 h. Of the 30% explants that survived this treatment, 33% were found to be stable tetraploids.

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