Leaf anatomy and photosynthetic acclimation in Valeriana jatamansi L. grown under high and low irradiance

Relationship of leaf anatomy with photosynthetic acclimation of Valeriana jatamansi was studied under full irradiance [FI, 1 600 μmol(PPFD) m-2 s-1] and net-shade [NS, 650 μmol(PPFD) m-2 s-1]. FI plants had thicker leaves with higher respiration rate (RD), nitrogen content per unit leaf area, chlorophyll a/b ratio, high leaf mass per leaf area unit (LMA), and surface area of mesophyll cell (Smes) and chloroplasts (Sc) facing intercellular space than NS plants. The difference between leaf thickness of FI and NS leaves was about 28 % but difference in photon-saturated rate of photosynthesis per unit leaf area (PNmax) was 50 %. This indicates that PNmax can increase to a larger extent than the leaf thickness with increasing irradiance in V. jatamansi. Anatomical studies showed that the mesophyll cells of FI plants had no open spaces along the mesophyll cell walls (higher Sc), but in NS plants wide open spaces along the mesophyll cell wall (lower Sc) were found. Positive correlation between Sc and PNmax explained the higher PNmax in FI plants. Increase in mesophyll thickness increased the availability of space along the mesophyll cell wall for chloroplasts (increased Sc) and hence PNmax was higher in FI plants. Thus this Himalayan species can acclimate to full sunlight by altering leaf anatomy and therefore may be cultivated in open fields