Tolerance of coffee (Coffea spp.) seeds to ultra‐low temperature exposure in relation to calorimetric properties of tissue water, lipid composition, and cooling procedure

Abstract

The effect of exposure to ultra‐low temperature (liquid nitrogen, LN) on viability of seeds desiccated to various water contents was investigated in 9 coffee species. Three groups of species could be distinguished based on seed survival after LN exposure. In group 1 species, no seedling production could be obtained after LN exposure due to endosperm injury. In group 2 species, recovery was very low or nil after rapid cooling, and only moderate after slow cooling. In group 3 species, very high percentages of seedling development were observed after both rapid and slow cooling. A high interspecific variability for the high moisture freezing limit was observed within the species of groups 2 and 3, since it ranged from 0.14 to 0.26 g H2O g−1 dry weight. A very highly significant correlation was found for those species between the unfreezable water content, as determined from DSC analysis, and the high moisture freezing limit of their seeds. No significant correlation was found between seed lipid content, which varied from 9.8 to 34.6% dry weight, and survival after LN exposure. However, a negative relationship was found between seed unfreezable water content and lipid content. Interspecific differences in fatty acid composition of seed lipids resulted in a high variability in the percentage of unsaturated fatty acids, which ranged from 28.7 to 54.4% among the 9 species studied. For all species studied, a highly significant correlation was found between the percentage of unsaturated fatty acids and the percentage of seedling recovery after rapid or slow cooling.

Optimal Hydration Status for Cryopreservation of Intermediate Oily Seeds: Citrus as a Case Study

“…This result was perfectly consistent with observations made in soybean seeds by Vertucci (1989a). Because they offer interesting applied perspectives, two other results of this study on coffee-seed tolerance to liquid nitrogen (LN) exposure have to be underlined (Dussert et al, 2001): (1) the unfrozen water content was negatively correlated with seed lipid content; (2) when expressed in terms of water activity, the interspecific variability for the higher limit was very low, suggesting that desiccating seeds below 75-85 % relative humidity (RH) allows them to reach directly the optimal hydration level for cryopreservation of non-orthodox oily seeds.…”

“…In the case of intermediate seed-propagated species, seeds are partially desiccation tolerant and, therefore, the option which has to be always tested first is whole seed cryopreservation. Using nine different coffee species, the basis of the limits of the hydration window for intermediate seed cryopreservation has been investigated recently (Dussert et al, 2001). When expressed in terms of water content, the higher limit of the hydration window was highly variable but corresponded always to the seed unfrozen water content (Vertucci, 1990), as determined by DSC analysis, suggesting that seed survival strictly depended on avoidance of intracellular ice formation.…”

Coffee seed physiology

“…Note that the lower limit of the hydration window for seed cryopreservation does not correspond to the level of seed desiccation tolerance (ô, control) when expressed in terms of water content. Adapted from Dussert et al (2001Dussert et al ( , 2003.…”

“…When expressed in terms of water activity, the interspecific variability in HL is very low, suggesting that desiccating under 75-86 % RH ensures an acceptable hydration level for the cryopreservation of Coffea seeds. Dussert et al (2001) classified the Coffea species in three groups. C. brevipes, C. canephora, C. liberica and C. stenophylla are part of Group 1, where no germination occurs after liquid nitrogen exposure, independently of water content or cooling procedure, although embryos extracted from cryopreserved seeds can germinate in vitro.…”

“…Using nine different coffee species, the basis of the limits of the hydration window for intermediate seed cryopreservation has been investigated recently (Dussert et al, 2001). When expressed in terms of water content, the higher limit (HL) of the hydration window is highly variable but corresponds always to the seed unfrozen water content (0.20 g of water per g dry weight, as reported by Eira et al, 1999a), as determined by DSC (differential scanning calorimetry) analysis, suggesting that seed survival depends on avoidance of intracellular ice formation (Vertucci, 1990).…”