Physiological Changes During the Germination of Cattleya aurantiaca (Orchidaceae)

Abstract

Se~s of Cattleya 011ra11t~aca grown ~ymbiotically on a medium containing sucrose as the sole source of organic carbon developed into leaf-bearing plants. Those sown on the same medium without sugar reached the protocorm stage but did not differentiate further. Cross transfers of seedlings between the two media indicated that following 21-30 days of growth on the sucrose-containing medium subsequent development may_proceed in the absence of sugar. Levels of chlorophyll and ribulose-1,5-diphosphate carboxylase were monitored and related to the ability of young seedlings to photosynthesize. A direct relationship between chlorophyll content and photosynthesis was not found. Increases in the activity of the enzyme were closely paralleled by increases in phdtosynthesis. A direct relationship was not found between chlorophyll a/ b ratios and photosynthetic capacity. Germinating seeds and seedli ngs grown in the absence of exogenous carbohydrate were unable to convert appreciable amounts of labeled acetate to sugar.

CARBON MOVEMENT BETWEEN HOST AND MYCORRHIZAL ENDOPHYTE DURING THE DEVELOPMENT OF THE ORCHID GOODYERA REPENS Br

“…These results suggest that a physiological change takes place in the mycorrhiza which stops movement of carbon from fungus to plant. The developmental stage at which this change takes place appears from our work to be much later than the development of the first leaf as suggested by Harrison & Arditti (1978) for a Cattleya sp. Although this change does not appear to be readily reversible (e.g.…”

“…It is not known whether mature photosynthetic orchids derive carbon via their endophyte. Harrison & Arditti (1978) found that uninfected seedlings of a Cattleya sp. were dependent on a source of external carbohydrate until they were about seven weeks old, when the appearance of the first leaf led to independence and autotrophic growth.…”

Photosynthesis of Young Orchid Seedlings

“…The pathway of carbon in very young protocorms of succulent orchids could well be a Cg photosynthesis. Harrison and Arditti (1978) recently measured the RUDP carboxylase activity in germinating Cattleya seedlings. The level of activity correlated well with the ability of the young seedling to photosynthesize.…”

“The orchids have been a splendid sport”—an alternative look at Charles Darwin's contribution to orchid biology

“…If the Cycnoches seeds contain as much lipid energy as fresh coconut solid endosperm (1470 kJ 100 g −1 ), the total is still a minuscule 212 kJ 14.4 g −1 or 0.000419618 kJ seed −1 . This assumption can be made because orchid seeds, like coconuts, are fatty in nature (Harrison, 1977; Harrison and Arditti, 1978; Arditti and Ernst, 1984) and may contain as much as 32% lipids (Knudson, 1929; Arditti, 1967, 1979, 1992) vs. 34% for coconuts.…”

“…Their seeds are small and balloon‐like (for reviews, see Arditti and Abdul Ghani, 2000; Yam et al, 2002a) and contain only limited food reserves (for reviews, see Arditti, 1992; Yam et al, 2002b). However, the seeds are also not equipped with the metabolic machinery required for the utilization of the starch and lipids they do contain (Harrison, 1977; Harrison and Arditti, 1978). During the early stages of germination they depend on fungi for nutrients.…”