AOBPreview originally published online on March 21, 2005
Annals of Botany 2005 95(7):1153-1161; doi:10.1093/aob/mci126
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Published by Oxford University Press on behalf of the Annals of Botany Company 2005
Optimal Hydration Status for Cryopreservation of Intermediate Oily Seeds: Citrus as a Case Study
1 Department of Crop Science, Faculty of Agriculture, UPM, 43400 Serdang, Selangor, Malaysia, 2 NHRI, 540, Tap-dong, Kwonsun-gu, Suwon 441-440, Korea, 3 IRD, UR141, 911 Avenue d'Agropolis, BP 64501, F-34394, Montpellier, France and 4 IPGRI, Via dei Tre Denari 472/a, 00057 Maccarese (Fiumicino), Rome, Italy
* For correspondence. E-mail dussert{at}mpl.ird.fr
Received: 23 September 2004 Returned for revision: 5 January 2005 Accepted: 7 February 2005 Published electronically: 21 March 2005
• Background and Aims The purpose of this study was to investigate the basis of the optimal hydration status for cryopreservation of intermediate oily seeds using Citrus as a model.
• Methods The relationships between equilibrium relative humidity (RH), seed water content, presence of freezable water as determined by DSC analysis, and germination percentage after immersion in liquid nitrogen (LN) were investigated in Citrus aurantifolia, C. grandis, C. madurensis and C. reticulata. The relationship between the lipid content of seeds and their unfrozen water content was also investigated.
• Key Results Independent of their level of seed desiccation tolerance, the optimal desiccation RH for seed tolerance to LN exposure was 75–80 % in the four species studied. This optimal hydration status always coincided with that at which presence of frozen water could not be detected in seed tissues during the cooling/thawing process. The unfrozen water content of seeds was variable between species and negatively correlated to seed lipid content. Using the present data, those obtained previously in seven coffee species and those reported by other authors for five other species, a significant linear relationship was found between the lipid content and the unfrozen water content of seeds.
• Conclusions This study provides additional evidence that intermediate oily seeds do not withstand the presence of freezable water in their tissues during the cooling/warming process. Moreover, it offers two important applied perspectives: (1) independent of their level of desiccation tolerance, testing germination of seeds of a given oily seed species after equilibration in 75–80 % RH at 25 °C and LN exposure, gives a rapid and reliable evaluation of the possibility of cryopreserving whole seeds of this given species; (2) it is now possible to calculate the interval of water contents in which non-orthodox oily seeds of a given species are likely to withstand LN exposure as a function of their lipid content.
Key words: Seed, intermediate, non-orthodox, Citrus, cryopreservation, water activity, relative humidity, desiccation, lipid content, DSC, ice, unfrozen water
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