Abstract：Xantha mutant 9388-1，a spontaneous mutant，was screened out from a normal green
leaf melon（Cucumis melo L.） variety‘ Baishami No.1’．Its contents of photosynthetic pigment and Chl
synthesis precursors，chlorophyll fluorescence kinetic parameters and ultra-structure of chloroplasts
were studied with mutant parent‘ Baishami No.1’ as contrast．The results showed that photosynthetic
pigment content in mutant leaves was significantly lower than that in‘ Baishami No.1’，while the ratio
between chlorophyll a and chlorophyll b was significantly higher than in‘ Baishami No.1’．Chlorophyll
biosynthesis was hampered at conversion from prophobilinogen（PBG） into uroporphyrinogen
（Urogen Ⅲ）．Compared with chlorophyll fluorescence kinetic parameters of‘Baishami No.1’，F0，
Pn，ФPS Ⅱ and ETR were significantly lower，while qN and NPQ were notably higher than that of
‘Baishami No.1’．There were no significant differences in Fm，FV/Fm and qP ．Under transmission
electron microscopy，9388-1 leaves were found with underdeveloped chloroplast，containing aberrant
thylakiods，fewer graum and starch grains than that of‘Baishami No.1’．Grana lamellae were deranged
with a line shape and less stacked，but grana lamellae was crowed together in normal one．These
results indicated that the biosynthesis chlorophyll was hampered，leading to aberrant chloroplast and the
photosynthetic pigments content changed，and then affected their stability．The mutant kept a higher
heat dissipation capacity，which could prevent photosynthetic apparatus from damaged by excessive
light energy and maintain the normal growth of plant.
