Harrison Hughes

Effects of PEG-induced water stress onin vitro hardening of ‘Valiant’ grape

Polyethylene glycol was added to the rooting medium ofmicropropagated grape shoots to induce water stress. At the end of the rooting stage, plantlets treated with 2% polyethylene glycol were compared with untreated control plantlets and greenhouse-grown plants. Leaves of treated plantlets had the highest deposition of epicuticular wax, followed by those of the greenhouse and control. Stomatal index did not vary among treatments. However, differences in leaf epidermal cell configuration were observed among treatments. The morphological changes of treated plantlets, including substantial deposition of epicuticular wax and modified leaf surface anatomy were associated with increasedex vitro survival after four weeks in the greenhouse.

Studies on stomatal function, epicuticular wax and stem-root transition region of polyethylene glycol-treated and nontreated in vitro grape plantlets

SummaryScanning electron microscopy, light microscopy, and gravimetric analysis was used to evaluate stomatal function, epicuticular wax, and the stem-root transition region of grape (Vitis sp. ‘Valiant’) plantlets grownin vitro, polyethylene glycoltreatedin vitro, and greenhouse-grown plants. Scanning electron microscopic studies of leaf surfaces ofin vitro-grown plants showed widely open stomata as compared to leaf stomata of polyethylene glycol-treatedin vitro-cultured and greenhouse-grown plants. Ultrastructurally, leaf epicuticular wax ofin vitro plants was less dense than in their polyethylene-treated and greenhouse counterparts. Quantitatively,in vitro-grown plants had reduced epicuticular was as compared to polyethylene glycol-treated and greenhouse-grown plants. Light microscopic studies showed no obvious differences in the vascular connections in the stem-root transition region ofin vitro-cultured, polyethylene glycol-treatedin vitro-cultured, and greenhouse-grown plants. It is therefore likely that the rapid wilting and desiccation observed after transplantingin vitro grape plantlets is due to their defective stomatal function and reduced epicuticular wax and may not be due to poor water transport associated with vascular connection.

Leaf anatomy and water loss of in vitro PEG-treated ‘Valiant’ grape

Polyethylene glycol was used to induce water stress of micropropagated ‘Valiant’ grape. Reduced growth and slow rooting were observed in treated plantlets with 2, 4 and 6% polyethylene glycol as compared to control plantlets with no polyethylene glycol in the rooting medium. At high concentrations of 4 and 6%, leaves exhibited wilting and necrosis. At the 2% level, plantlets recovered and grew satisfactorily. Detached leaves of treated plantlets with 2% polyethylene glycol lost less water than controls when exposed to low humidity for 4 hours. Leaf anatomy of plantlets treated with 2% polyethylene glycol, control (in vitro plantlets) and greenhouse-grown plants were compared under light microscopy. Leaves from control plantlets contained larger mesophyll cells, lacked normal palisade layer formation, had greater intercellular pore spaces and fewer chloroplasts. Leaves from polyethylene glycol-treated plantlets, however, had smaller mesophyll cells, a more defined palisade layer, reduced intercellular pore space and the greatest number of chloroplasts. These results suggest that an osmoticum such as polyethylene glycol may be used to induce more normal leaf anatomy and reduced water loss in micropropagated ‘Valiant’ grapes.

Water loss and polyethylene glycol-mediated acclimatization of in vitro-grown seedlings of 5 cultivars of date palm (Phoenix dactylifera L.) plantlets.

Plantlets derived from shoot-tips of seedlings from five cultivars of date palm, Phoenix dactylifera L., were subjected to polyethylene glycol in liquid medium. Comparisons of water loss of detached leaves among in vitro-grown, polyethylene glycol-treated and greenhouse-grown plants showed significant differences with treatment for all cultivars studied. For each treatment, significant differences were also found among cultivars. The common result was that the percent of moisture loss of non-treated in vitro-grown plantlets was almost twice that of greenhouse-grown plants. Polyethylene glycol-treated plantlets showed a water loss of approximately 27%, similar to that of greenhouse plants as compared to an average of 40% in control plants. This demonstrates the possibility of using polyethylene glycol as an osmoticum for in vitro acclimatization of plantlets prior to transfer to soil.

In vitro acclimatization of date palm (Phoenix dactylifera L.) plantlets: A quantitative comparison of epicuticular leaf wax as a function of polyethylene glycol treatment.

Wax deposits on leaf surfaces ofin vitro-grown plantlets,in vitro plantlets treated with polyethylene glycol and greenhouse-grown seedlings from five cultivars of date palm (Phoenix dactylifera L.) were extracted and quantified. Significant variations among treatments and cultivars were obtained. Greenhouse-grown plants had the greatest wax deposits followed by the acclimatized plantlets.In vitro plantlets had an average of 15% of the wax of greenhouse plants. Cultivar and plant age differences had a significant effect on the quantity of wax deposits. Greenhouse seedlings of ’Majhool’, ’Deglet Noor’ and ’Khadraoui’ (cultivars grown under irrigation) had less wax accumulation than ’Zahidi’ and ’Sayer’, dryland cultivars.The increase in wax deposition as a result of polyethylene glycol treatment, explains in part, the decreased water loss observed in acclimatized plantlets when transferredex vitro.

Micropropagation of Phytolacca dodecandra through shoot-tip and nodal cultures.

A procedure for micropropagation of endod (Phytolacca dodecandra) is described. BA at 0.44 μM produced 3.1 new shoots per expiant in six weeks using shoot tips. Nodal expiants, however, produced up to 4.7 shoots per explant on medium with 0.44 μM BA and 0.27 μM GA,. IBA at 0.49 μM induced 90% rooting with minimal callus. Plantlets were successfully transferred to the greenhouse and some staminate clones produced flowers after six months.

An Efficient In Vitro Propagation Protocol of Cocoyam [Xanthosoma sagittifolium (L) Schott]

Sprouted corm sections of “South Dade” white cocoyam were potted and maintained in a greenhouse for 8 weeks. Shoot tips of 3–5 mm comprising the apical meristem with 4–6 leaf primordial, and approximately 0.5 mm of corm tissue at the base. These explants were treated to be used into the culture medium. A modified Gamborgs B5 mineral salts supplemented with 0.05 μM 1-naphthaleneacetic acid (NAA) were used throughout the study. Thidiazuron (TDZ) solution containing 0.01% dimethyl sulfoxide (DMSO) was used. Erlenmeyer flasks and test tubes were used for growing cultures. The effect of different media substrate, thidiazuron, and the interaction between TDZ and Benzylaminopurine (BAP) on cocoyam culture were tested. Results indicated that cocoyam can be successfully micropropagated in vitro through various procedures. All concentrations tested (5–20 μM BAP and 1–4 μM TDZ) produced more axillary shoots per shoot tip than the control without cytokinins. Greater proliferation rates were obtained through the use of 20 μM BAP and 2 μM TDZ, respectively, 12 weeks from initiation. Shoots produced with BAP were larger and more normal in appearance than those produced with TDZ, which were small, compressed, and stunted. The use of stationary liquid media is recommended for economic reasons.

Comparative Growth Analysis and Acclimatization of Tissue Culture Derived Cocoyam (Xanthosoma sagittifolium L. Schott) Plantlets

The current study was carried out to compare the external leaf structure of tissue culture-derived and conventionally-propagated Cocoyam [ Xanthosoma sagittifolium (L) Schott] plantlets and to develop an efficient acclimatization protocol for these plantlets. Acclimatization studies were carried out during winter and summer to ascertain seasonal influence relative to plant survival upon transfer from in vitro to natural conditions. Results indicated that, cocoyam leaves have few stomates on both abaxial and adaxial surfaces with fewer on the adaxial surface. High levels of epicuticular wax (EW) found in vitro may have contributed to reduced transpiration rates. The reduced amounts of EW on acclimatized plants could be attributed to the rapid cell enlargement in expanding leaves, more rapid than the rate of wax formation. Acclimatization using humidity tent decreased leaf wilting