Explants of Actinidia deliciosa Chev. Liang and Ferguson var. Hayward were cultured in controlled CO2 atmospheres in the presence of different sucrose concentrations. Organogenesis was measured after 45 days in explants from the different assays, and quantification of photosynthesis, transpiration, chlorophylls, RUBISCO and total soluble protein content was performed in leaves from the different treatments. The best results were those of explants cultured at 600 &mgr;mol CO2 mol-1 on 20 g l-1 of sucrose for the first 20 days and then transferred to sucrose-free medium until the end of the culture period. Increasing CO2 to 2000 &mgr;mol CO2 mol-1 in the atmosphere of the culture vessel reduced all the parameters studied. Photosynthesis of autotrophically developed explants trebled that of the reference heterotrophic explants, as there was an apparent inverse relationship between photosynthesis and transpiration. Photosynthesis was saturated at 300 &mgr;mol m-2 s-1 PPFD and 600 &mgr;mol CO2 mol-1. Chlorophylls and RUBISCO presented differences between treatments, mainly between different CO2 concentrations, with the highest values in autotrophically cultured explants. Explants grown at 2000 &mgr;mol CO2 mol-1 showed the lowest RUBISCO/Prots ratio, probably due to negative adaptation of RUBISCO to long-term high CO2. In short, explants grown in a controlled microenvironment, with increased CO2 and under autotrophic conditions, developed wholly functional photosynthetic apparatus well prepared to be transferred to ex vitro conditions, which has many advantages in micropropagation.

In traditional in vitro culture, the low CO 2 concentration inside the vessels restricts photosynthesis and necessitates the addition of sucrose to the culture medium as the main energy source, thus bringing about changes in the absorption of mineral elements from the culture medium. In this study, we investigated macronutrient absorption and sugar consumption in Actinidia deliciosa Chevalier Liang and Ferguson cv. Hayward (kiwi), cultured on medium supplemented with varying amounts of sucrose (0, 10, and 20 g l −1 ) under both heterotrophy and autotrophy, flushed with different concentrations of CO 2 (non-ventilation, 300, 600, and 2,000 μl l −1 ). In ventilated systems with 20 g l −1 of sucrose, sucrose absorption was less than under non-ventilation. The lowest rate of sucrose absorption was recorded when the explants were cultured on medium supplemented with 20 g l −1 of sucrose and flushed with 600 μl l −1 CO 2 . Absorption of NO 3 − , PO 4 3− , and Mg 2+ were high (maximum) at the end of the culture period (40 d) in explants flushed with 600 μl l −1 CO 2 that have been cultured 20 d in the presence of sucrose and then transferred to a sucrose-free medium. These autotrophic conditions promoted maximum plant growth in terms of both fresh and dry mass as well as the length and number of shoots and leaves. The study shows that to maintain an optimum regime of mineral nutrition for prolonged culture of kiwi in vitro, an increased amount of these three ions should be supplemented in Murashige and Skoog's medium.

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The relationship between polyamines and ethylene is controversial because the degree of interference of one pathway with the other may differ according to species, stage of development and experimental procedure. In this paper, we modify ethylene biosynthesis by the addition of aminoethoxyvinylglicine (AVG) or 1-aminocyclopropane-1-carboxylic acid (ACC) and study how it affects polyamine content and development of kiwifruit explants (Actinidia deliciosa CS Liang. & AR Fergusson). Cultured under ventilation where ethylene did not accumulate in the culture vessels, kiwi explants had higher ACC synthase activity and lower polyamine content than those grown without ventilation. In explants cultured in the reference medium, putrescine was the more abundant polyamine and spermine was only detected in the free fraction irrespective of ventilation. Under ventilation, addition of ACC to the culture medium inhibited organogenesis, there was less spermidine and spermine was not detected. Addition of AVG to the culture medium increased both the number of shoots and the amount of polyamines, and inhibited ACC synthase, so S-adenosylmethionine (SAM) led to increasing synthesis of spermidine and spermine. The increase in putrescine is more difficult to explain on the basis of inhibition of ethylene biosynthesis. The increase in the number of shoots in kiwi explants due to AVG addition may be attributed to the lack of ethylene in the atmosphere of the vessels or the increase in free polyamines.

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