Tuesday, April 22, 2014

Pollination Videos

Here's the link to the BBC pollination video collection, and below is some spectacular footage from Louie Schwartzberg's film, "Wings of Life," which is now on Netflix!


Wednesday, March 12, 2014

Gibberellic acid and starch hydrolysis

So in lab two weeks ago we saw some unexpected results in our gibberellic acid (GA) experiments...to refresh your memory, let's look at slides from Lab 6.


We had plates with starch agar, and plates with starch agar + GA. Seed halves (with and without embryo) were assigned to quadrants in each plate. (It's important to note that when we split our barley seeds in half, the embryo half would still have some endosperm/starch, as seen above, and would also retain some of the aleurone layer -- we didn't perfectly isolate the embryo.) We then stained the plates with iodine to look for presence of starch hydrolysis -- which would show up as "halos" (see below) of light-colored agar where starch had been hydrolyzed into glucose molecules (which do not stain black with iodine like starch does).
 Starch + GA plate with "hydrolysis halos"

We also looked at the GA-->hydrolysis pathway from another angle -- accumulation of glucose (as opposed to absence of starch).


We did this with barley seed halves as before, but then we tested for presence of glucose using Clinistix test strips.

So what would be our expected results from these experiments? Something like this, right?

Without the embryo to release the signal molecule GA, embryo-less seed halves on the starch plate would have no "trigger" to initiate production of alpha-amylase, the enzyme that facilitates starch hydrolysis. But when we provide that hormone on the starch + GA plate, even embryo-less barley halves should show signs of hydrolysis. (We'll just worry about presence/absence of hydrolysis now, not relative intensities or halo size.)

Same idea here: without GA, the embryo-less seed halves won't hydrolyze any starch (thus, there shouldn't be any significant level of glucose when we test for it).

But this isn't what we saw in lab, was it? No! We saw (with a few "correct" exceptions) high glucose levels in all tubes, and hydrolysis halos in all treatments! What's up with that??

Of course we could have mixed up our seed halves, right? That hilum can be hard to distinguish sometimes. But many of the seed halves on the agar plates had begun to germinate, allowing us to double-check ourselves -- and all the ones I checked were correct (also, the Tuesday labs saw similar results). Perhaps some groups, when cutting their seeds, included a small portion of the scutellum (where the GA is released from), in their embryo-less halves. Contamination or mixing of plates/tubes could also be an issue, but likely it has more to do with processes going on in the seeds themselves. Most importantly, it's likely that some early germination processes had been initiated in many of the barley seeds, perhaps by storage in a humid environment, so some amount of GA had actually already been sent to the aleurone layer, promoting the production of alpha-amylase and beginning the starch hydrolysis process in the endosperm. Thus, even in our embryo-less / endosperm halves, we were seeing evidence of alpha-amylase activity through starch reduction and glucose accumulation.

Here we just looked at presence/absence of starch hydrolysis. What hypotheses would you make about relative intensities of this process among the different treatments (we talked about this a bit in class)? i.e., which halos would be bigger? where would we find more or less glucose?



Plants in Motion

Here's the link to Indiana University's Plants in Motion Theater 

You can find analogous videos on YouTube, but this is a good starting place to get an appreciation for how much these supposedly sessile organisms can move!

Tuesday, March 11, 2014

Photosynthesis resources

Let's face it. Photosynthesis is confusing. Here are some resources to help you figure it out.

A handy 4-page PDF that outlines the major reactions, and includes some questions to test your understanding.

This is a massive list of online resources regarding photosynthesis. They're sorted by category (Overview, Light-Independent Reactions, etc.) and compiled by profs at Arizona State and University of Illinois.

If you find any of these particularly helpful, comment below!

-jb

Monday, March 10, 2014

Science Job Resources

This warm weather is making me think of all the awesome summer field biology jobs that will be starting soon. These are great ways to learn about experimental design and help tackle important questions in the natural sciences, and also to discover fascinating regional flora and fauna! Here are a few of my favorite list-servs and job boards:

EcoLog: click here to sign up for this awesome list-serv, which sends you a daily list of job announcements, interesting articles and engaging discussions in the world of ecology. (But be sure to select Digest as the Subscription Type, or else you'll get LOTS of separate emails each day). 

ConBio: the Society for Conservation Biology hosts this job board, which is another great resource.

Texas A&M: another good job board (and not just for jobs in Texas!)

SCA: the federally funded Student Conservation Association has a host of neat positions available. Let me know if you want more info about this program.

Archbold Biological Station: this private research station in Central Florida has great post-baccalaureate internships in a wide range of areas, from herpetology to avian epidemiology to plant ecology. This is a great opportunity to do independent research, and as an ABS Plant Lab alum, I can tell you that it's one of the best opportunities out there for young scientists.

- jb

Saturday, February 22, 2014

Gravitropism in Lateral Roots

Ryan brought up a very good point when we were looking at root caps on Thursday -- does the root cap on a lateral root contain statoliths? Remember, statoliths are those starch-filled organelles thought to be involved in gravitropism, or the plant's ability to sense the earth's gravitational pull and respond accordingly (ie, roots go down, shoots go up). Statoliths are found in cells called statocytes.



In the germination videos we saw earlier, we see that lateral roots don't start growing straight down -- they tend to grow out away from the primary root. This makes sense, right? If all the roots responded in a similarly strong way to the pull of gravity, we'd have our whole root system growing straight down in a mass of parallel roots! Then the plant would be missing out on exploiting all those nutrient-rich pockets of soil that are located all around it -- it would only be taking advantage of the nutrients held in the soil directly below. So it would behoove a plant to direct its root growth in response to a more complex function of gravity + nutrient availability + water + avoidance of obstacles, not just gravity. (As always, it's more complicated than it seems at first glance!) And this is what we see in more detailed studies of root system development, though the primary root does seem to be mainly influenced by gravitropism. But the seemingly different growth of lateral roots has received less attention. In this paper, researchers examined the development of gravisensitivity in lateral roots of Arabidopsis.

While gravitropism has been extensively studied in the primary root, the response of lateral roots to gravitropic stimuli has poorly been described. It has been assumed that the molecular mechanisms are similar to what occurs in primary roots. However, this response is species-dependent: in some species lateral roots are unresponsive to gravity [] while in others lateral roots grow at a set angle relative to the gravity vector, a response known as plagiogravitropism []. This indicates that lateral roots have an endogenous (genetic) programme for gravitropism that has been selected to optimize root system architecture depending on each species' ecological niche and lifecycle. (Guyomarc'h et al. 2012)

Gravisensitivity has been recorded in primary roots even prior to germination. What this study found was that, yes, lateral root caps do have statocytes and functioning statoliths, but the gravitropic response in lateral roots seems to be delayed when compared to primary roots, with the lateral roots seeing reorientation after ~12-24 hours.

An earlier study found that in Arabidopsis, some lateral roots are just "programmed" to grow horizontally rather than vertically. These lateral roots still showed gravitropism -- if you tilted the plant, the lateral roots would reorient to their original plane of growth -- but they grew at what researchers call a gravitropic set-point angle which was not straight down. You can think of this like a compass responding to the Earth's magnetic field -- the primary root grows south, while a lateral root might grow south-east. Going in either direction would require "evaluating" the earth's magnetic field, but the responses to that evaluation would be different. In plants, they're responding to gravity instead of magnetism, and not sending all of their roots in the same direction. Which makes sense -- if we're performing a search-and-rescue, we wouldn't send everyone out due north, would we? We'd send groups of searchers in a number of directions to increase our search area. Plants are doing the same thing, but searching for water and nutrients, and avoiding competitors and obstacles.

Pull up any plant and you'll see that root system development is dependent on a number of factors beyond simply up vs down. Here's a good article reviewing root system architecture.

Germination!

Below are some cool germination videos. The first shows hypogeal germination of runner bean (Phaseolus coccineus) seeds, and the second shows epigeal germination of Phaseolus vulgaris, the common string bean. Look at those lateral roots! Do your remember what latent meristematic tissue those arise from? What other morphological features can you identify?



Pondering Plants

Hello budding botanists!

I've been meaning to set this blog up for a while now, but haven't gotten around to it til today. This will be a place for me to post interesting videos, links and articles, and hopefully provide answers to some of the questions that pop up in class but I don't know off-hand. Feel free to leave comments or send me links you think would be of interest to the class!

See y'all in lab,

jb