|Abstract or Summary
- The metabolism of Strongylocentrotus purpuratus (Stimpson)
was investigated at several levels of urchin organization. Some experiments
were performed with tissues from recently collected
(acclimatized) urchins, Other experiments were performed with tissues
from urchins held at one of two temperatures (acclimated) for
Body-component oxygen consumption was measured for bodywall,
gut, testis, and ovary slices from seasonally acclimatized and
temperature-acclimated urchins. Metabolic rates of testis and ovary
underwent seasonal shifts appearing to compensate for changes in
habitat temperature -- i. e., higher and lower rates during cold and
warm periods, respectively. Rates of body wall and gut underwent
seasonal shifts in a direction opposite those of testis and ovary -- i. e. ,
inverse compensation. This gonadal-nonreproductive difference was
observed less conclusively with temperature-acclimated urchins.
Compensatory shifts occurred with testis. Equivocal shifts occurred
with body wall, gut, and ovary. Inverse compensation of metabolic
rate resulted when oxygen-consumption measurements were repeated
with gut slices and homogenates from temperature-acclimated urchins.
Radiotracers glucose-1-¹⁴C, glucose-6-¹⁴C, and acetate-
1-¹⁴C -- were incubated with gut, testis, and ovary homogenates from
temperature-acclimated urchins. Cold acclimation caused higher
CO₂ and lower lipid activities in the testis. Conversely, warm acclimation
caused higher CO₂ and lower lipid activities in the gut. Conversion
of glucose to CO₂ was greater in gut than in testis. Conversion
of acetate to lipid was generally greater in testis than in gut.
Phosphogluconate oxidation and lipid synthesis relative to glycolysis
and oxidation, respectively, increased in the testis following warm
acclimation. Conversely, glycolysis and oxidation relative to phosphogluconate
oxidation and lipid synthesis, respectively, increased in
the gut following warm acclimation. Cold acclimation resulted in
higher levels of glycogenesis for testis and ovary but in equivocal
differences for gut.
Cytochrome c oxidase activity was determined in gut, testis,
and ovary extracts from seasonally acclimatized and temperatureacclimated
urchins. Changes in enzyme activity paralleled those in
the oxygen-consumption and radiotracer results. Gut activity was highest in September, whereas testis and ovary activities were highest
in December and March, respectively. Gut activity was higher
following warm acclimation, but testis and ovary activities were
higher following cold acclimation.
Glucose 6-phosphate dehydrogenase (G6PDH) activity was determined
in gut, testis, and ovary extracts from temperature-acclimated
urchins. Changes in G6PDH activity were the reverse of those in the
oxygen-consumption, radiotracer, and cytochrome c oxidase results,
suggesting that changes in the effectiveness with which glycolysis and
phosphogluconate oxidation compete for the common substrate,
glucose 6-phosphate (G6P), may compensate for each other. Warm
acclimation generally increased gonadal G6PDH activity but failed to
alter gut activity. Gonadal G6PDH activity was generally much higher
than was that of the gut. The apparent G6PDH-G6P affinity for gut,
testis, and ovary was increased following cold acclimation.
Body-component weights were determined from the urchins used
in the metabolic rate-season studies. Gonadal ash-free dry weights
expressed as a percentage of the total were maximal in the fall and
minimal in the spring, whereas those of the body wall were maximal
in the spring and minimal in the fall. Seasonal changes in the gut were
negligible by comparison.
The above temperature-induced changes in urchin metabolism
are discussed relative to temperature-induced changes in whole-urchin
metabolism and to situations confronting intertidal populations of
urchins. Gonadal catabolism appears maximal in the winter or spring
and minimal in the fall, whereas gonadal anabolism appears maximal
in the fall and minimal in the spring. Nonreproductive catabolism
appears maximal in the fall and minimal in the winter, whereas
nonreproductive anabolism appears maximal in the spring and minimal
in the fall.