Please use this identifier to cite or link to this item: https://scholarbank.nus.edu.sg/handle/10635/149414
Title: DEVELOPMENTAL AND MORPHOLOGICAL STUDIES ON THE EPIPHYTIC FERN PYRROSIA PILOSELLOIDES (L.)
Authors: CALVIN KOH KOK KENG
Issue Date: 1996
Citation: CALVIN KOH KOK KENG (1996). DEVELOPMENTAL AND MORPHOLOGICAL STUDIES ON THE EPIPHYTIC FERN PYRROSIA PILOSELLOIDES (L.). ScholarBank@NUS Repository.
Abstract: The present study showed that sporophytes of P. piloselloides with different mature sterile frond shapes could be catagorised broadly as sun-growing and shade-growing populations, based on the light environment and several physiological parameters. The observed variation in frond morphology could be mainly attributed to the prevailing light conditions in which the ferns were growing. The results obtained indicated that fronds grown in low light were lanceolate in shape while those growing in high light, rounder. Based on the results obtained from studies on spore germina- tion, populations of P. piloselloides with different frond shapes did not arise as a result of interspecific hybridisation or other cytological aberrations. Thus, changes in frond size could be an adaptation of the fern to capture available light, for its survival and growth. Optimal sterlisation procedure to obtain the highest number of germinated spores was established in this study. The growth and development of gametophytes of P. piloselloides was fol- lowed and found to be similar to the other Polypodiaceous ferns. Five developmental stages were observed, and they culminated in the production of one sporophytic initial per gametophyte. The gametophytes were able to withstand unfavourable cultural conditions (e.g. submergence and overcrowding) and subsequently resumed normal growth. Gametophytes of P. piloselloides were also shown to possess a notable ca- pacity to withstand desiccation for as long as 60 days; they were capable of regenerat- ing new tissues even after such long duration of drought. CAM was not operating in gametophytes of P. piloselloides. Only the sporo- phytic generation exhibited the CAM-mode of photosynthesis. CO2 did not affect spore germination. In a CO2-free environment, germinated spores were able to grow for two weeks by relying on the stored reserves within the spore. Gametophytic development was also shown to be accelerated under CO2- enriched environments. This also resulted in an earlier transition of the gametophytic stage to the sporophytic stage. Concomitant with the accelerated development, greater biomass accumulation as a result of higher photosynthetic rates was observed. Higher photosynthetic rates resulted in greater amount of starch accumulation in the chloroplasts of gametophytes cultured in elevated CO2. However, such starch accu- mulation did not result in a decrease in photosynthetic rates. In the present study no acclimation of the photosynthetic process was observed. This was also indicated by the highest efficiency of light utilisation by gametophytes grown under elevated CO2 levels. Dark respiration rates also increased under high CO2; this could result from the demand for greater structural growth and maintenance of the gametophytes.
URI: http://scholarbank.nus.edu.sg/handle/10635/149414
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