ABSTRACT
Lettuce is one of the most consumed leafy vegetables in the world (MartínDiana et al. 2007). Ÿere are di•erent varieties of lettuce each with particular morphological characteristics (Di Benedetto 2005). Among them, butterhead lettuce is one of the most spread varieties all over the world. Ÿe lettuce head is an assemblage of heterogenic morphological leaves that are packed together over the growing point of the plant. Its formation results from the
18.1 Introduction 171 18.2 Materials and Methods 173
18.2.1 Plant Material and Sample Preparation 173 18.2.2 Determination of Chlorophyll Content 173 18.2.3 Determination of Color Coordinates 174 18.2.4 Statistical Analyses 174
18.3 Results and Discussion 174 18.3.1 Chlorophyll Content 174 18.3.2 Color 176
18.4 Conclusions 178 Acknowledgments 178 References 178
accumulation of young leaves under the layers of leaves covering the growing point (Wien 1997). Ÿis growth pattern determines that leaves formed by different tissues, not only with di•erent maturity degree, but also with di•erent metabolic and physiological activities, and exposed to di•erent environmental conditions coexist within a plant. So the lettuce plant is an interesting biological model where it is possible to evaluate these factors simultaneously in each unit.