Infraspecific variability in the volatile leaf oils of Chamelaucium uncinatum (Myrtaceae)

Variation in leaf essential oils and morphometric characters among 38 locations of Chamelaucium uncinatum were used to describe infraspecific diversity and geographic patterns of variation. Four chemical types were designated: citronellal, -pinene or limonene dominant, or one in which all three monoterpenes were co-dominant. The citronellal and limonene types were geographically restricted but the -pinene and co-dominant types were widespread. The citronellal type also demonstrated higher diversity (by Shannon–Weiner index) in the oil profile than the other types. Biochemical differentiation was not strongly paralleled by morphological differences between chemotypes; only the citronellal-type differed morphologically from the other three types with respect to floral bud and leaf characters. Based on biochemical and morphological differences, and geographic localization, it was concluded that the citronellal type may represent a recently evolved ecotype of C. uncinatum.     

Leaf temperature of desert sand dune plants: perspectives on the adaptability of leaf morphology

The leaf temperature of six annual and six perennial plant species was monitored during spring and summer on a sand dune ecosystem in the delta Mediterranean coast of Egypt. During winter, leaves of all tested perennial species attained temperatures higher than the air temperature at night and shortly after sunrise, with maximum leaf–air temperature differences reaching up to 8°C. The lowest differences were less than 1°C. Around noon, the leaves of several species attained temperatures lower than that of the air whereas others showed higher temperatures. The opposite was true during summer, when leaf temperatures were lower than air temperature. The maximum leaf–air temperature differences occurred after midnight towards sunrise and reached up to 10°C. The lowest differences were found around noon and were of less than 5°C. The annual plant species have more pronounced variations than perennials in their leaf temperatures during the night and for most of the day. The leaves were heated or cooled a few degrees above or below the air temperature. The results are discussed in relation to the morphological characters of the leaves. The variation in leaf temperature at different times of the day was significantly related to leaf morphology, specific leaf area, thickness, volume, leaf area index and the surrounding environment.     

Effect of IAA on symbiotic germination of an Australian orchid and its production by orchid-associated bacteria

Seven isolates of orchid-associated bacteria (OAB) belonging to five species were tested for their effect on mycorrhiza-assisted germination of the terrestrial orchid Pterostylis vittata. Hormone standards were also tested to evaluate their potential roles in the germination and development of the orchid. Strains of Pseudomonas putida, Xanthomonas maltophilia and Bacillus cereus promoted symbiotic germination, whereas certain strains of P. putida and an Arthrobacter species reduced it. Symbiotic germination was enhanced by IAA, inhibited by gibberellic acid and suppressed by kinetin. Each species of OAB produced IAA, although the conditions of growth affected the production of the auxin. IAA was not produced by the mycorrhizal fungus from P. vittata under the test conditions. Enhancement of symbiotic germination development may have resulted either from the production of IAA by the OAB and/or by the induction of endogenous hormones in the orchid by the metabolites of the bacteria and/or mycorrhizal fungus.     

Secobeyerene diterpenes from Beyeria calycina

Two new secobeyerene acids have been isolated from Beyeria calycina var. minor and their structures identified as ent-6α,17-dihydroxy-3,4-secobeyer-15-en-3-oic acid and (4S)-ent-18-hydroxy-3,4-secobeyer-15-ene-3,17-dioic acid. Distinct pathways are involved in the formation of the former compound and the major seco acid component.     

Histochemical Study of Photoperiodic and Low Temperature Effects on Floral Induction of Spinacia oleracea

Shoot apices of Spinacia oleracea plants have been induced toflower either by: (a) subjecting leaves to 24 h long day, or(b) exposure to a short photoperiod but displaced by 8 h (displacedshort day) in the usual 24 h short-day cycle, or (c) exposureto low temperature (5 °C) during the dark period of thenormal short day. A quantitative cytochemical assay of pentosephosphate pathway activity during floral induction indicatesan approximate doubling of the rate of activity when comparedto that of vegetative apices (short day) (21 °C). Exposure to either low temperature, or a displaced short photoperiodstimulates pentose phosphate pathway activity in the shoot apexin a manner similar to that seen by long-day induction. Thischange in metabolic activity is accompanied by changes in theshape of the shoot apex which resembles that seen at an earlystage during floral induction. Spinacia oleracea, pentose phosphate pathway, shoot apex, glucose-6-phosphate dehydrogenase, floral induction, chilling, displaced short day