Leaf Morphological Ultrastructure, Chlorophyll Biosynthesis And Photosynthesis Of The Yellow-leaf Mutant Of Rosa Beggeriana

Rosa Beggeriana is wild rose species with strong cold, drought and disease resistances, originatingfrom Xinjiang. The yellow-leaf mutant of R.Beggeriana was obtained by using the treatment of gammaray. It was named as ‘golden rose’ with the stably hereditary golden leaves. Although it’s growthpotential is weaker than R.Beggeriana, and even occasionally with sun-burn phenomenon, it can grownormally and maintain the golden-yellow or greenish-yellow leaves in the whole growth season.Obviously, the mutant can be used as colorful ornamental shurubs directly, or as a new germplasmresource by introgressing the golden leaf color into the new rose variety. Before the genetic mappingand the cloning of the color mutant genes and the further application of this germplasm, the basicstudies on the morphology and physiology of the mutant are very necessary.In Comparison to R.Beggeriana, the leaf morphological structure, chlorophyll biosynthesis andphotosynthetic characteristics of the yellow-leaf mutant had been investigated in order to explore thepossible morphological and physiological reason of the yellow-leaf color, as well as the photosynthesisand its photoprotective mechanisms in the mutant. The main results are listed as follows.1. Compared with R.Beggeriana, the LAM of the mutant was significantly decreased. The upperepidermal hair of leaf disappeared, and the lower epidermal hair became scarce. The leaf cuticle and cellwall were significantly thinned. The sizes of palisade tissue cells of the yellow-leaf mutant were smallerthan R.Beggeriana, and the numbers of chloroplast of palisade tissue cells were significantly reduced.Ultrastructural observation showed the mutant has the intact chloroplast structure as R.Beggeriana,which the thylakoids system included the stroma lamellae and grana lamellae. However, the decreasedconcentrations of chloroplast stroma lamellae, the less numbers and loosely arrangements of thelamellaes were observed in the mutant. The phenomenon of chloroplast swelling were also found in themutant. The total chlorophyll contents of the mutant were significantly decreased. The contents ofchlorophyll precursors of ALA, PBG, UrogenIII and CoprogenIII were also decreased significantly. Theactivities of the key enzyme ALAD and UROS were decreased but not significantly.2. Diurnal changes of photosynthesis of R.Beggeriana and the mutant all showed as a single-peakcurve. Pn of the mutant were lower than that of R.Beggeriana in spring, and the decline of Pn of themutant was due to stomatal limitation from9:00to11:00while non-stomatal limitation after11:00inspring. Pn of the mutant were also lower than that of R.Beggeriana in autumn, and the difference weremore significant in autumn. But the decline of the mutant was mainly caused by non-stomatal limitationin autumn. The Fo value of the mutant was significantly lower than R.Beggeriana.Their Fv/Fm valueswere0.78and0.76in wild species and the mutant respectively. The diurnal changes of Fv’/Fm’、ΦPSⅡand qP were all firstly increased and then decreased, and reached the lowest values at noon. However,the NPQ values were firstly decreased till noon then increased in the afternoon. The NPQ value of themutant was higher than R.Beggeriana, which reached the significant level at9:00and13:00.3. The DEPS values were zero in both wild species and the mutant at early morning. But theirDEPS values increased but there was no significant difference between wild species and the mutant at noon. However, the VAZ value of the mutant decreased significantly compared with the mutant.4. In comparison to the wild species R.Beggeriana, the activity of POD of the mutant wassignificantly higher at9:00, but its activities of CAT was significantly lower after11:00. Moreover, theactivity of APX and GR of the mutant were significantly higher at9:00, but its activities of APX wassignificantly lower after15:00. The contents of AsA and the AsA/DHA of the mutant were allsignificantly higher than R.Beggeriana after11:00, but its content of GSH、GSSG and the GSH/GSSGwere significantly higher than R.Beggeriana at11:00. The contents of H2O2had no significantdifference, but the contents of MDA of the mutant were significantly higher than R.Beggeriana duringthe most daily time.