Micropropagation and comparative growth analysis of in vitro and ex vitro cultured cacti.

摘要

Conventional propagation methods are not suitable in most cases for rare cacti because they usually have limited reproductive capacities and show extreme slow growth. Research in this dissertation was devoted to applying in vitro culture techniques to develop a micropropagation and regeneration system for three rare and endangered cacti species. Regenerated and re-established plants were obtained for Coryphantha minima and Obregonia denegrii. Combinations of 0.5 mg l{dollar}sp{lcub}-1{rcub}{dollar} benzyl adenine (BA) with 0.1 mg l {dollar}sp{lcub}-1{rcub}{dollar} naphtalene acetic acid (NAA) or 10 mg l{dollar}sp{lcub}-1{rcub}{dollar} kinetin(KIN) with 1 mg l{dollar}sp{lcub}-1{rcub}{dollar} indole acetic acid (IAA) resulted in superior shoot proliferation. In addition, massive production of somatic embryos with BA-NAA combinations was observed in Obregonia denegrii which could also be established into full grown plants. Although spontaneous in vitro rooting occurred with both species, ex vitro root induction offered superior results for subsequent acclimatization of shoots. Unfortunately, micropropagation was unsuccessful for Ariocarpus agavoides due to poor and inconsistent morphogenetic responses during in vitro culture.; In developing micropropagation systems for cacti, certain variables were considered so that these techniques could be used in less developed countries where endangered species often occur. This included varying the levels of sugars and nutrients in the culture medium and reducing the relative humidity inside culture vessels. Effects of these variables on growth and photosynthetic activity in vitro were analyzed and compared to cacti cultured ex vitro. Unlike normal, C3 plants, cacti possess a CAM physiology which alters patterns of carbon uptake that can affect growth responses in tissue culture. In vitro derived plantlets of Coryphantha minima were seven fold larger than plants cultured ex vitro during the same time period. Gas exchange analysis and daily fluctuations of malic acid revealed that the in vitro environment stimulated photosynthetic activity, with cacti showing a net increase of CO{dollar}sb2{dollar} uptake in the dark and light. It was also shown that high humidity in the culture vessel affected transpiration rates and, consequently, stomatal opening, which resulted in greater CO{dollar}sb2{dollar} uptake of cacti cultured in vitro. The acclimatization of in vitro derived cacti to ex vitro conditions was facilitated by plant succulence which delayed excessive water loss. Additionally, tissue cultured cacti retained the capacity to generate normal levels of epicuticular wax upon removal from the culture vessel which prevented drastic water loss and aided acclimatization.