Possible correlation between increased vigour and chitinase activity expression in tobacco

Abstract

Nicotiana tabacum (tobacco) plants with several-fold increased chitinase enzyme activity levels were obtained through transformation with a Zea mays (maize) chitinase cDNA clone, Ch2, under the control of the CaMV 35S promoter. There was a linear correlation (r=0.74, P=0.009) between the endochitinase activity and the weight of homozygous seedlings grown in the greenhouse in some experiments. Progeny seedlings of self-pollinated regenerants (heterozygous for Ch2) grown for 18 d in Petri plates could be separated into vigorous and non-vigorous categories based on size, which were predicted to be 2n or 1n and null, respectively, for Ch2. Testing showed that the visually estimated vigour of these progeny co-segregating for Ch2 and nptll generally correlated with resistance to kanamycin and chitinase activity. There was also a correlation between growth and chitinase activity in suspension cultures derived from transgenic and wild-type when measured after 20 d. Twelve-day-old wild-type and transformed seedlings grown in soil under culture room conditions in closed plastic containers were visibly taller and had higher seedling weights than their counterparts grown under mist in the greenhouse. Likewise, the chitinase activity in the cell wall-bound proteins of the faster growing seedlings was more than double that of the greenhouse-grown seedlings. While these studies do not always demonstrate the correlation between vigour and chitinase activity, overall, they do support the hypothesis that chitinases have a role in plant growth.