MRI can reveal metabolic changes in lily bulbs in vivo during dormancy release

The factors influencing dormancy release in lily bulbs strongly affect commercialization success, but the mechanism of dormancy release is still unclear. Magnetic resonance imaging (MRI) can detect changes in morphology and water status in a living plant bulb and aid in investigating release factors. To evaluate whether MRI could be used to detect intra-bulb metabolic changes during the dormant period in Oriental Lilies (Lilium 'Sorbonne'), a series of MRI and sugar concentration measurements were performed weekly on bulbs stored for 11 weeks at 4°C. The image quality of intra-bulb structure obtained using T 1-weighted imaging was superior to that obtained using T 2 -weighted imaging and had a higher signal-to-noise ratio (0.97±0.01). Magnetization transfer ratio values for the bud and basal plate declined during the first eight weeks of cold storage (P>0.05), and were well correlated with concentration of soluble sugar in the bud (R 2 =0.95) and basal plate (R 2 =0.93). Thus, MRI can serve as a valuable tool for observation and analysis of dynamic morphological and metabolic changes in vivo during dormancy release. This information is potentially useful as a guide in the improvement of horticultural product quality.

Respiratory Response of Dormant Nectarine Floral Buds on Chilling Deficiency

Changes in main biochemical respiratory pathways in dormant nectarine floral buds were studied with nectarine trees （Prunus persica.var, nectariana cv. Shuguang） in order to determine the function of respiration in dormancy release. Oxygen-electrode system and respiratory inhibitors were used to measure total respiratory rates and rates of respiratory pathways. Results showed that chilling deficiency blocked the transition of respiratory mode, and made buds stay in a state of high level pentose phosphate pathway （PPP） and low level tricarboxylie acid cycle （TCA）. The decline of PPP and activation of TCA occurred synchronously with the release of dormancy. In addition, the inhibition of PPP stimulated a respiration increase related with TCA. It could be concluded that the function of PPP activation in dormancy release might be limited and PPP declination inducing TCA activation might be part of respiration mode transition mechanism during bud sprouting.

Respiratory Response of Dormant Nectarine Vegetative Buds to High Temperature Stress

High temperature stress （HT） is efficient in breaking endo-dormancy of perennial trees. The effects of HT （50°C） on the respiration of dormant nectarine （Prunus persica var. nectariana cv. Shuguang） vegetative buds were evaluated in the research. We found that bud respiration was transiently inhibited by HT and the pentose phosphate pathway （PPP） and the cytochrome C pathway （CYT） were significantly affected. On the substrate level, PPP was activated in the HT-treated buds compared with the control group. However, the activation did mot occur until hours after HT treatment. The tricarboxylic acid cycle （TCA） in both the HT-treated buds and in the control group proceeded at a low level most of the time compared with total respiration. On the electron transfer level, CYT was transiently inhibited by HT but became significantly active in the later stage. CYT operation in the control group exhibited an attenuation process. The alternative pathway （ALT） fluctuated both in the HT-treated samples and in the control. The results suggest that the temporary CYT inhibition and the following PPP activation may be involved in HT-induced bud dormancy release and budburst mechanisms.

Photothermal controls of vegetative dormancy in Poa secunda

Background:Summer vegetative dormancy is a desirable trait in cool-season grasses when they are interplanted with annual crops.Sandberg bluegrass(Poa secunda J.Presl.)shows summer dormancy,but the environmental cues that control dormancy remain unknown.Methods:A controlled environment study using temperature and day length combinations of 32.2℃/15 h,26.6℃/14 h,21.1℃/13 h,and 15.5℃/12 h was conducted with P.secunda accessions PI232347,PI639272,and PI232348,and‘Audubon’red fescue as a nondormant control to determine the optimum treatment for dormancy induction.A second study using treatments of 26.6℃/14 h,21.1℃/13 h,and 15.5℃/12 h was conducted to determine the thresholds for dormancy release.A third study used a factorial experiment with two temperatures(32.2℃ and 15.5℃)and two day lengths(15 and 12 h)to differentiate between temperature and day length effects on dormancy induction.Results:Of the four temperature and day length combinations,all except for 15.5℃/12 h resulted in dormancy by the end of 6 weeks,with 32.2℃/15 h inducing dormancy in only 17 days.Of the three treatments for dormancy release,15.5℃/12 h broke dormancy the fastest in all accessions and released the most number of plants from dormancy.Considerable variation existed between accessions for the speed of dormancy release in the 21.1℃/13 h and 26.6℃/14 h treatments.The third study showed that temperature is the primary inducer for summer dormancy,while longer day length may promote dormancy under inductive temperatures.Conclusions:This study identified the optimum photothermal for induction and release of summer dormancy in P.secunda,which will help future studies in elucidating the mechanism of summer dormancy.