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Imaging fluorometry was applied to investigate the tolerance of Japanese honeysuckle ( Lonicera japonica Thunb.) of different ploidy levels to heat stress. Seedlings of L. japonica, the diploid cv. Damaohua and the tetraploid cv. Jiufengyihao, were exposed to heat stress of 42 °C for 6 h and a recovery for 10 h. Heat stress significantly decreased maximum photochemical efficiency, electron transport rate, effective quantum yield of photosystem 2, and photochemical quenching of both cultivars, but it decreased the non-photochemical quenching (NPQ) only in the tetraploid. Heat stress increased the content of total soluble sugars, proline, and malondialdehyde in both cultivars while it increased NPQ only in the diploid. Our findings suggest that the tetraploid showed to be more resistance to heat stress than the diploid of L. japonica, which was indicated by different chlorophyll fluorescence imaging techniques and metabolic changes. Moreover, the degree of recovery in the tetraploid was higher than that of the diploid. The tetraploid also possessed thicker epidermis (both upper and lower) and palisade tissue as well as denser pubescence. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle ( Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O3) exposure (70 ng g−1, 7 h d−1 for 31 d). Net photosynthetic rate ( PN) of both cultivars were drastically ( P<0.01) impaired by O3. Although there were significantly positive correlation between PN and stomatal conductance ( gs) in both cultivars under each treatment, the decreased gs in O3 might be the result rather than the cause of decreased PN as indicated by stable or increasing the ratio of intercellular to ambient CO2 concentration( Ci/ Ca). PN under saturating CO2 concentration ( PNsat) and carboxylation efficiency (CE) significantly decreased under O3 fumigation, which indicated the Calvin cycle was impaired. O3 also inhibited the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm), actual quantum yield of PSII photochemistry (ΦPSII), electron transport rate (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), the maximum in vivo rate of Rubisco carboxylation (Vcmax) and the maximal photosynthetic electron transport rate (Jmax) which demonstrated that the decrease in PN of the honeysuckle exposed to elevated O3 was probably not only due to impairment of Calvin cycle but also with respect to the light-harvesting and electron transport processes. Compared to the diploid, the tetraploid had higher relative loss in transpiration rate ( E), ( gs), ( PNsat), Vcmax and Jmax. This result indicated that the Calvin cycle and electron transport in tetraploid was damaged more seriously than in diploid. A barely nonsignificant ( P=0.086) interaction between O3 and cultivar on PN suggested a higher photosynthetic sensitivity of the tetraploid cultivar. [ABSTRACT FROM AUTHOR]