Physiological Characteristics and Leaf Ultrastructure of a Novel Chlorophyll-deficient chd6 Mutant of Vitis venifera Cultured in vitro

A novel chlorophyll-deficient chd6 mutant of F₁ hybrids from Vitis venifera was selected to study its primarily physiological characteristics and leaf ultrastructures under culturing in vitro. The results showed that although increasing Fe²⁺ and Mg²⁺ concentration could improve growth of the mutant in vitro, the effect was limited. In addition, it was determined that relatively lower Fe²⁺ and Mg²⁺ concentrations would be beneficial to the survival in vitro on GS medium. Chlorophyll contents of the mutant were significantly lower than those of its parents (4.53–13.76% of those of the higher-value parent Red globe). The chlorophyll a/b ratio was greatly increased (up to 4.34) to approximately twofold greater than that of its parents. Some critically successive enzymes for converting ALA to chlorophyll a could be inhibited to a variable extent in the chd6 mutant, and more serious inhibition could happen in critical enzymes converting Mg-proto to Pchlide or Mg-proto to chlorophyll b. The mutant also showed not only poor Rubisco activities, lower percentage of dry matter, and soluble carbohydrate content, but also lower IAA and GA (GA₁ + GA₄) content and higher ABA content. In leaf ultrastructures, the mutant presented larger stomata size, higher percentages of stomata opening, and lower stomata density with more stoma approximately a ring shape. Most chloroplasts of the chd6 mutant developed as asymmetric ellipses with deficient and irregular lamella.