Cotyledonary explants of 4-day-old Cucumis melo cv. 'Hale's Best Jumbo' in vitro seedlings showed maximum initiation of shoot buds when cultured onto a revised Murashige & Skoog medium supplemented with 5/~M indole-3-acetic acid and 5/~M benzylaminopurine and cultured at 25-29°C under low light intensity (5-30#molm-2s-~). Subculture of the shoot buds onto the same medium without auxin and supplemented with 3 #M benzylaminopurine caused the development of shoots from 30% of the buds. The presence of abscisic acid significantly increased the number of explants producing shoot buds. Bud initiation was affected by genotype, seedling age, light intensity, and temperature. Addition of gibberellic acid, thidiazuron or silver nitrate to regeneration medium did not improve either bud initiation or shoot regeneration.

Cucumber green mottle mosaic virus is reported for the first time from Australia. It was detected in watermelons (Citrullus lanatus) affected by a severe mosaic and stunted foliar development near Katherine in the Northern Territory. Tobamovirus morphology was initially detected in leaf sap by electron microscopy, and species identity confirmed by genetic tests.

The effect of maturation on the morphological and photosynthetic characteristics, as well as the expression of two genes involved in photosynthesis in the developing, current year foliage of Eastern larch (Larix laricina [Du Roi]) is described. These effects were observed on foliage during the third growing season after grafting of scions from trees of different ages onto 2 year old rootstock. Specific leaf weight (gram dry weight per square meter), leaf cross-sectional area (per square millimeter), and chlorophyll content (milligram per gram dry weight) all increase with increasing age in long shoot foliage from both indoor-and outdoor-grown trees. Net photosynthesis (NPS) (mole of CO2 per square millimeter per second) increases with age on indoor-but not outdoor-grown trees. NPS also increases with increased chlorophyll content, but outdoor-grown scions of all ages had higher chlorophyll content, and chlorophyll does not appear to be limiting for NPS outdoors. To extend these studies of maturationrelated differences in foliar morphology and physiology to the molecular genetic level, sequences were cloned from the cab and rbcS gene families of larch. Both cab and rbcS gene families are expressed in foliage but not in roots, and they are expressed in light-grown seedlings of larch but only at very low levels in dark-grown seedlings (-2% of light-grown seedlings). Steadystate cab mRNA levels are relatively higher (-40%) in newly expanding short shoot foliage from juvenile plants compared to mature plants. Unlike cab, the expression of the rbcS gene family did not seem to vary with age. These data show that the maturation-related changes in morphological and physiological phenotypes are associated with changes in gene expression.

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