Abstract
The electrical conductivity of leachates from imbibing seeds has been used as a vigor test for several species. The adaptation of this methodology to different species requires knowledge on the leaching kinetics of electrolytes. For Brazilwood seeds, the classic method was not satisfactory and rapid tests are essential because they have low storage capacity at room temperature. Leaching kinetics during seed imbibition is a function of physiological quality, presence or absence of seed coat, imbibing temperature and the initial moisture content of seed. In this study, the electrolyte leaching rate of six different categories of seeds, from two regions, was evaluated in seeds with and without seed coat and incubated with different moisture contents and at different temperatures. The results showed that the electrolyte leaching rate in Brazilwood seeds is independent of the physiological quality, the presence or absence of seed coat and imbibition temperature, but these factors changed the total amount of electrolytes leached. The leaching rate increased in the first few minutes of imbibition, suggesting that the adjustment of the methodology must consider the reduction in imbibition time, reduction in temperature, use of a controlled and slower pre-imbibition, and replacement of the imbibition solution after the first few minutes.
Highlights
Seed samples taken from batches containing a large proportion of dead seeds or seeds that produce abnormal seedlings often show considerable leaching of solutes when imbibed in water, which is probably caused by the presence of many damaged cells (Matthews et al, 2012)
For Brazilwood seeds, after 10 minutes of imbibition, on average, the electrolyte leaching had reached about 20% of the total leaching within the 24 hours recommended by the test (Vieira, 1994), and after 60 minutes they had reached 37%, that is, 50 minutes after the first evaluation, there was an increase of only 17% in leaching (Figure 1)
The results showed that the lowest electrolyte leaching rates occurred for seeds with seed coat and lower imbibition temperature (Figure 2)
Summary
Seed samples taken from batches containing a large proportion of dead seeds or seeds that produce abnormal seedlings often show considerable leaching of solutes when imbibed in water, which is probably caused by the presence of many damaged cells (Matthews et al, 2012). Seed solutes consist mainly of amino acids, nucleic acids and lipids which have electrolytic properties that can be determined by measuring their electric charges (Krzyzanowski et al, 1991). The increase in conductivity of the imbibition solution, i.e., the reduction in the electrical resistance caused by the electrolyte leached from the seed tissues to water can be used as a diagnostic test of vigor loss and degree of deterioration (Vieira, 1994). The imbibition temperature and seed coat cracks may change electrolyte leaking (Carvalho et al, 2009; Ribeiro et al, 2009). Measuring the electrical conductivity of the seed imbibition solution to evaluate vigor and degree of deterioration relies on methods that avoid the influence of other variables on the results. One of the first steps to do so is to understand the leaching kinetics of these electrolytes when seeds are subjected to different procedures
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