Lecture notes and gists, provided for remediation due to the CUPE 3903 strike.
30 March Lecture Gist
Reviewed briefly the concepts of dormancy and seed banks, before presenting a case study on extreme dormancy: Lotus (Nelombo nucifera) seeds that remain viable for up to about 1300 years. Much of the dormancy must be due to the thick and impermeable seed coat of the lotus, as well as its location (peat): Both desiccation and especialy gas impermeability would minimize residual metabolism and the possibility of oxidative damage.
Dormancy break is also obviously important. Aphanes was used as a case study. This is an 'upside-down' case study, because Aphanes is a therophyte that usually germinates in the fall, rather than in the spring, so temperature cues are the opposite of what we would expect. Seeds were collected and stored in soil, replicating natural storage conditions. Germination tests provided moisture and controlled temperature. The data is presented in the scanned lecture notes available below (remediation_lecture02).
27 March Lecture Gist
Referred to Dr. Kyle Belozerov's lecture, his comment about the 18th century notable (Goethe) who recognized that plant development involves metamorphosis, in which (for example) leaves metamorph into flowers, etc. Showed part of Goethe's Die Metamorphose der Pflanzen describing the seed, with its foreshadowed pattern of root, leaf and germ (embryo).
Described the approximately three structure/function of the seed: the seed coat (protection), the embryo and endosperm, emphasizing that food storage for growth of the germling can be the cotyledons of the embryo and/or the endosperm. Showed examples of seeds (cucumber, carrot, bean, castor bean, maize) to give an idea of the diversity of form.
Posed as a wind-dispersed seed to illustrate that control of when (and where) a seed germinates is central to species survival. Introduced the concept of a seed bank and showed data for northern temperate hardwood forests (see seed biology overheads and
Second Set of Lecture Notes
remediation_lecture02.The examples of dormancy and relation to long-term survival included elderberry, birch, sedge, goldenrod and red maple. Each provides a unique example: There's no one size fits all rule, but dispersal, presence in the seed bank, longevity and the ecological habitat all play roles.
A suitable question for the final exam will involve the interplay of seed bank and seed dormancy for a northern temperate woodlot/meadow species.
25 March Lecture Gist
Dr. Kyle Belozerov gave a guest lecture on homeotic genes (Plant and Animal Development: Homeotic Genes). First, he highlighted their structure and role in animal development using the ubx mutant of Drosophila as an example. Then, he described their structure and function in floral development using Arabidopsis as an example. There are both similarities and differences in the nature of homeotic genes in plants and animals. While the number of homeotic genes in plant floral development is fewer than the number that function in animal embryogenesis, they operate in a collaborative rather than autonomous manner to control the development of carpels, stamens, petals and sepals.
Here are my notes for Dr. Belozerov's lecture [pdf], and Dr. Belozerov's lecture slides [pdf].
23 March Lecture Gist
Explained the 'triage process' we are undergoing as lab exercises are removed due to the continuing strike. Answered practical questions from students about the worst case scenario of no more lab exercises (already completed work, up to the seedless vascular plant exercise, will be calculated using the original weightings, then adjusted to a percentage).
Reminded students of the problem of 'self-sex' in plant reproductive biology. Both morphological difference (pin and thrum) and self-incompatibility are important ways to avoid inbreeding. But what about the 'animal answer': sex chromosomes?
Showed detailed data on the frequency of perfect (hermaphrodite) flowers, monoecious and dioecious, emphasizing the very low frequency of dioecious (which can indeed be caused by sex chromosomes).
Described some of the research that is done on sex chromosomes in plants. Unlike insects and animals, for which sex chromosomes appeared very early (500 to 1000 million years ago), sex chromosomes in plants are rare, and appear to be the result of genetic degeneracy. Posed the question: are organisms with sex chromosomes (including humans) genetically degenerate?
Students were invited to compose questions for the final exam, and did so (on the study of sex chromosomes in plants and perfect flowers).
Moved to the next topic: embryogenesis. Starting from the single-cell zygote, the first division lays down a polar axis, followed by multiple cell divisions that --at the octant stage-- includes a protoderm. Subsequent major developmental stages are globular, heart-shaped, and mature form. Differentiated bwteen dicotyledon and monocotyledon groups. Showed mutants that are due to the loss of one of the three major segments of the mature embryo: radicle, hypocotyl, and cotyledon(s). These are due to homeotic gene mutants. Homoeotic genes play a central role in animal develoment as well.
20 March Lecture Gist
Reminded students of the issue we were exploring: avoiding 'self-sex' in plant reproductive biology. Morphological difference (pin and thrum) are not a sufficient guarantee. Genetic control must also occur.
Self-compatibility and self-incompatibility in higher plants is controlled by the so-called S-locus (where S stands for self). Two general genetic mechanisms exist: 1) gametophytic and 2) sporophytic. Explained how they work, and emphasized that the sporophytic self incompatible mechanisms relies on a 'pollen diploid phenotype' because of sporophytic material on the outer coat of pollen. Noted the difference in how pollen tube growth is inhibited (RNAase versus inhibition of pollen hydration) and the signaling mechanism of sporophytic self incompatibility (glycoprotein and receptor kinase).
Addressed the relevance and importance of incompatibility mechanisms in the context of crop breeding, explaining the concept of hybrid vigour.
Students were invited to compose questions for the final exam, and did so (on how pollen tube growth is inhibited and farming hybrid crops).
First Set of Lecture Notes
remediation_lecture01.pdf18 March Lecture Gist
I explained to students the impact of the strike: lecture is fine, lab exercises depend on if and when a settlement is reached. As labs become delayed, pollen identification will be dropped, followed by pollen tube growth, followed by fruit/vegetable dissection/anatomy, followed by flowering plant dissection/anatomy.
The 60/40 split of lecture/lab will be retained, with the lab mark based on graded material (Photosynthesis Write-Up / Algae Drawing / Quiz 1 -- Algae and Fungi / Fermentation / Microscope Use / Seedless Vascular Plants -- Drawing)
Recapped where we were in the 'Life of a Plant', basically reviewing floral morphology / pollination etcetera, then began to explore selfing and inbreeding versus outcrossing in plants, to emphasize the importance of a plant not having sex with itself.
