Structure and Development of Crop Plants

Non-Technical Summary:<br/>
My lab will study the structure and development of spinach leaves of plants grown under various nitrogen fertilization levels, to understand the microscopic basis of spinach leaf breakage and, in collaboration, how this is related to susceptibility to bacterial infection. The other major goal is to try to understand the differences between almond varieties that show more skin breakage after processing and the varieties that are resistent to this damage.
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Approach:<br/>
Obj. 1 (spinach): Anatomical and cytological studies of the internal structure of spinach leaves will be conducted according to published methods (Ruzin, 1999). Cell wall components such as cellulose, hemicellulose, pectins, lignin, callose and suberin will be targeted using specific histochemical stains. Light microscopic analyses will be performed in the Jernstedt lab. Leaves will be collected from treatments varying in nitrogen fertilization rates, and greenhouse and field-grown material will be compared. Scanning electron microscopy of leaf surfaces will be used to examine epidermal characters that may be involved in leaf textural changes. Spatial relationships between cell types and tissues will be analyzed using laser scanning confocal microscopy with computer algorithms.
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Obj. 2 (almond nuts): Anatomical and cytological studies of the internal structure of almond seeds (kernels) will be conducted according to published methods (Ruzin, 1999). Developmental anatomy of almond seeds collected at weekly and bi-weekly intervals after pollination will be studied using paraffin and resin sections for light microscopy. Cell wall components such as cellulose, hemicellulose, pectins, lignin, callose and suberin will be targeted using specific histochemical stains. Light microscopic analyses will be performed in the Jernstedt lab. Almond seeds will be processed in the Barrett lab in Food Science, with variation in temperature and moisture treatments of particular interest.
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Progress:<br/>
2012/01 TO 2012/12<br/>
OUTPUTS: Collaboration with Food Science Ph.D. student, Megan Clements, in an interdisciplinary study of postharvest handling of almond kernels, led to investigations of almond seed coat structure, development and persistence, with the long term goal of improving the quality of commercially available shelled almonds while maintaining processes instituted to ensure food safety. Unintentional almond skin separation is a defect according to the USDA grading standards, and significantly reduces the selling price. The tissue-level mechanism of almond skin separation is not addressed in the literature; it is known that the residual endosperm layer detaches from the embryo (specifically the cotyledons), but not how, why, or in response to what threshold of postharvest processing. It is possible that while almonds seeds are growing, there are periods of vulnerability when key tissues are developing. During these times, stressful growing conditions could predispose almonds to skin separation. The purpose of this research was to observe the incremental tissue changes that occur during blanching as a model system for skin separation, and to establish when during the growing season those tissues are developing and, therefore, when they may be more vulnerable to environmental stressors. Immature Nonpareil almonds were harvested every two weeks upon cessation of endosperm expansion, and then sampled twice a week from the date the embryos had reached full size and until maturity.
<br/>PARTICIPANTS: Dr. Eduardo Gutierrez, former Ph.D. student Megan Clements, current Ph.D. student Dr. Trevor Suslow, Cooperative Extension Specialist, Departmentof Plant Sciences, UCD Dr. Diane Barrett, Cooperative Extension Specialist, Department of Food Science.
<br/>UCD TARGET AUDIENCES: Ph.D. student Megan Clements and Dr. Diane Barrett reported results to meetings of the California Almond Board.
<br/>PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
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IMPACT: Immediately after blanching, almond seed coats appeared larger than the kernels within them. After soaking overnight, almond kernels had swollen along with their seed coats, and fit tightly within their seed coats again. At each blanching temperature (70, 80, 90, and 100 degrees C), the mean fraction of separated seed coat increased with blanching duration along a logistic sigmoidal curve. Blanching progressed more slowly at lower temperatures. All seed coats were separated after about 50 seconds of blanching at 90 degree C and 100 degree C, and after 3.5-4 minutes at 80 degree C, whereas blanching at 70 degree C required 7-9 minutes to completely remove seed coats. Blanching rates ranged from 0.171-0.384 sec-1 at 100 degree C, from 0.125-0.271 sec-1 at 90 degree C, 0.039-0.087 sec-1 at 80 degree C and 0.011-0.016 sec-1 at 70 degree C. At each time and temperature combination, the five almonds evaluated typically did not respond to the blanching treatment in a uniform fashion. For example, it was common for complete seed coat separation to occur in one or more of the almonds, while others had incomplete separation. This variation in the response of individual almonds is likely due to exposure to many small differences in growing conditions, slight maturity differences or variability in postharvest stress exposure. Microscopic studies of almond kernels at different stages of development documented stages of seed coat formation and maturation. One week post-bloom, integuments were 7-20 cell layers thick, uniform, and undifferentiated from each other. Both were present, but no recognizable boundary existed between the integuments, except for some separation between the edges of the inner and outer integuments at the micropylar tip. By 16 weeks post-bloom, the embryo (the future kernel) had enlarged sufficiently to displace the endosperm in most, but not all of the sampled population. Cotyledon parenchyma cells had not yet accumulated the majority of their energy stores by this time As evidenced by increased staining in later samples, cells filled up with storage products over the month between 16 and 20 weeks, until they stained densely from 20 weeks onward.