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  • Author or Editor: Farida Safadi x
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Detached and intact leaves (first fully expanded leaf from the top) of tobacco (Nicotiana tabaccum L.) plantlets hardened in vitro with 2.0% polyethylene glycol (PEG) showed increased diffusive resistance (r) over those of nonhardened plantlets as measured by a steady state porometer. The leaves of the PEG hardened plants maintained a higher resistance throughout the one hour dessication period in approximately 30% relative humidity although both treatments showed an increase in diffusive resistance after 30 minutes. This indicates that the stomates are functioning in the in vitro tobacco plantlets. The higher (r) in the PEG treated plants may be due to more complete closure of stomates, higher cuticle wax content or a combination of both.

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Research involving acclimatization of in vitro plantlets by reducing the relative humidity (RH) in vitro requires a suitable method for monitoring RH in the culture vessels. In this research we describe a method for measuring the RH dynamically in the culture vessels, based upon thermocouple psychrometry. Thermocouple junctions (.003 mm gauge) were used with a wet cotton thread on the wet bulb junction inserted from the side of the jar. Aspiration was provided by tiny fans run by miniature motors left outside the vessels. Pre-calibrated aspirated and non-aspirated experiments showed realistically reduced RH in the cultures covered with caps which allowed for gas exchange. The aspirated procedure resulted in greater precision. This procedure with some refinement could be a useful method for monitoring RH in in vitro cultures.

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Previous studies have shown that liquid medium additions on established cultures enhance shoot growth and proliferation. In the present report, the growth and multiplication of apples and grapes were evaluated after the addition of liquid media to established cultures. Grapes and apples were micropropagated on agar solidified nutrient medium with 5μM BAP, and 4.4μM BAP, 1.4μM GA, 4.9μM IBA, respectively. A liquid overlay of similar medium was added after 4 to 6 weeks in both cultures. Improved growth, number of shoots, and a reduction in callus growth were observed in both species as compared to shoots transferred to fresh solid media. The number of micropropagated apple shoots and their height increased significantly by 35% and 69% respectively. Proliferation of grape shoots increased by 198% while callus growth decreased by 64% when compared to cultures transferred to fresh solid media.

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