A review of dipterocarps - Center for International Forestry Research
A review of dipterocarps - Center for International Forestry Research
A review of dipterocarps - Center for International Forestry Research
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Seed Physiology 63<br />
Table 4. Lowest-safe moisture content values (wet weight basis) <strong>for</strong> mature seeds*.<br />
Species Source LSMC (%)<br />
Dipterocarpus alatus** Tompsett (unpub.) 25<br />
Shorea siamensis Tompsett (unpub.) 51***<br />
Shorea singkawang Yap (1986) 55<br />
Shorea xanthophylla Tompsett (unpub.) >41***<br />
Stemonoporus canaliculatus Tompsett (unpub.) 43***<br />
Vatica umbonata Mahdi (1987) 74****<br />
*: no slopes and intercepts available <strong>for</strong> these species;<br />
**: seed is OLDA (orthodox with limited desiccation ability);<br />
changes accompanying loss <strong>of</strong> viability <strong>of</strong> S. robusta<br />
have also been reported (Nautiyal et al. 1985).<br />
Some authors have confused the effects <strong>of</strong><br />
desiccation itself with the effects <strong>of</strong> ageing; in order to<br />
determine the effects <strong>of</strong> ageing, moisture contents<br />
should be kept constant. However, in studies by Song et<br />
al. (1983) on Hopea hainanensis it is clear that<br />
desiccation effects per se were being examined. At 36%<br />
moisture content the ultrastructure was intact, but on<br />
desiccation to 26% moisture content, which severely<br />
reduces germination percentage, various changes were<br />
observed. Vesicles appeared in the cytoplasm, vacuolar<br />
membranes ruptured and cell contents became less<br />
distinct. Cell walls and cytoplasm became separated and<br />
nuclear membranes could not be distinguished from the<br />
nucleolus. These changes illustrate a general<br />
deterioration <strong>of</strong> cellular structure rather than an effect<br />
confined to the cell membrane. In a further study (Song<br />
et al. 1986), desiccation to 31% was shown to disturb<br />
the ribosomes and endoplasmic reticulum, but these<br />
changes were reversed on re-hydration.<br />
More recently, Krishan Chaitanya and Naithani<br />
(1994) measured changes in superoxide, lipid<br />
***: based on at least 25 seeds per germination;<br />
****: unusually high value.<br />
peroxidation and superoxide dismutase <strong>for</strong> seeds <strong>of</strong> S.<br />
robusta during desiccation. They concluded that the loss<br />
<strong>of</strong> viability observed may be caused by the cumulative<br />
effect <strong>of</strong> peroxidation products <strong>of</strong> polyunsaturated fatty<br />
acids and peroxidation <strong>of</strong> the membrane lipids.<br />
Storage Physiology<br />
Some aspects <strong>of</strong> seed storage are considered elsewhere:<br />
practical aspects, including the effects <strong>of</strong> gases, are<br />
discussed in Chapter 4; chilling physiology is considered<br />
above under germination effects. Topics discussed below<br />
include the following: best recorded storage periods; use<br />
<strong>of</strong> viability constants; the significance <strong>of</strong> oil contents;<br />
some aspects <strong>of</strong> tissue culture; and various associations<br />
with storage physiology.<br />
Best storage records<br />
An up-to-date summary <strong>of</strong> best storage records is given<br />
in Table 5. These records should not be confused with<br />
practical recommendations; if the recommended storage<br />
conditions were employed, longer storage would be<br />
expected in many cases. The best record <strong>for</strong> an OLDA<br />
species is 2829 days <strong>for</strong> Dipterocarpus alatus and the