RSS

Zombie Plants – The Green Undead Awaken on Halloween (if it rains)

21 Oct

 

(More technically, Poikilohydric Species play possum)

This week’s fieldtrip is tomorrow, so with no crystal ball, so I’m taking a little pre- trip literally to the back yard.   Today we’re talkin’ plants with no roots and no internal plumbing, or almost none.    All water goes in through the foliage as it rains, but when dry the plants look and act like death, until resurrection when soggy returns.     Although there is a spectrum of possibilities and variation in mechanisms,  the interesting cases are not mere wilting or  closing up shop, but rather extreme deeply suspended animation, essentially lifeless.   You wonder how long a plant in that state can rise from the grave.  Answer: long.

Remember the term poikilohydric (= plant zombie).

Florida is a great place to encounter these resurrecting oddballs.   We have a lot of epiphytes, some of which behave poikilohydrically, most famously our Resurrection Fern (Pleopeltis polypodioides) as photographed by John Bradford:

Spanish-Moss and its cousin Ball-Moss (Tillandsia recurvata) may not be full-blown dry-and-diers, but they get mighty thirsty hung out to dry.

img_4279

Ball-Moss on tree trunk

These species use umbrella-shaped scales (think micro-toadstools for second analogy in one sentence) to capture and distribute rainfall.

poikilohydry-tillandsia-us-bw

The scales on Spanish-Moss leaf.  By Robert Wise, Ph.D., Univ. WI Oshkosh, with permission. Scanning electron microscope. The scale is anchored like a toadstool at the middle.

One drop can irrigate an entire scaly leaf as we will see momentarily.  The scales have intricate structure, and flip down in the presence of water.  Water moves from scale to scale like an electric current traversing a wire.  Watch this video of one drop going a long way. CLICK TO SEE!

What is so astonishing is the depths of the Snow White slumber.  Hard-core cases go through profound internal biochemical and structural reduction and disassembly.  Internal membranes collapse or disappear.   Special protective proteins, enzymes, and electrolytes form.  Internal cellular components vanish.  Some go so far as to dismantle their photosynthetic apparatus, and reconstruct it upon remoistening.    Seen with a microscope the leaf cells look deceased.  Then it all comes back.

Below is a series of photos of a liverwort from a tree in my yard.  After the photo showing the liverwort on the hot dry bark are three microscope views of the same leaf at the same magnification, the first snapshot while dry, the 2nd  photo 15 minutes after re-moistening, and the third shot about an hour later.   Notice that in the dry condition the cells look hollow with no apparent chloroplasts (the green disks in the later photos).  The chloroplasts are either gone  or collapsed into a thin film against the outer walls of the cell.   Yet just minutes post-moistening chloroplasts appear magically, and after an hour the previously deadish cells look perky.

poikilohydry-liverwort-on-tree-expanded

Liverwort on hot dry tree trunk

poikilohydry-liverwort-leaf-dry

A dry leaf, microscope view, from the liverwort.  Notice the hollow “empty” cells.

poikilohydry-liverwort-leaf-wet-15-minutes

Fifteen minutes after wetting.  Chloroplasts (little green dots) already returning!

poikilohydry-liverwort-approx-one-hour

About an hour later

The reappearance of chloroplasts is a jiffy.  What is truly mind-boggling after wetting, however, is the instant return of respiration, intake of oxygen and expulsion of carbon dioxide, such as our breathing.    In their dry state poikilohydric plants show no detectable, biological activity.    Within seconds of rewetting carbon dioxide exhales.  (The very first carbon dioxide given off is probably not from metabolism, but merely forced out of nooks and crannies by the wetting, then metabolic carbon dioxide from life renewed follows in a few more seconds.) The graph below shows warp-speed carbon dioxide release by a remoistened moss.   So fast it’ll make your head spin.

poikilohydry-dry-moss03

Rapid carbon dioxide release.   Moistening was at about 650 seconds.  The fast dip happened as the water was squirted onto the dry leaf, perhaps from the gases in the pipette.  The mall first peak near 700 seconds is probably non-metabolic carbon dioxide, followed by the broader breath of metaboliic carbon dioxide as Rip Van Winkle awakens.  No time wasted!

Why that burst happens is not well understood.  I mean, why would the plant start respiring, burning sugars, before it is ready to replensih its own sugars by photosynthesis.  One line of thought is metabolism revs up like “gentlemen start your engines” before the transmission engages, that is, before all the plant’s membranes and internal structures return to working capacity.    The slumbering plant needs to work fast to exploit a fleeting cloudburst.

poikilohydry-cladonia

Poikilohydric lichens by John Bradford, followed below by moist and dry Selaginella by JB.

The distribution of plants with poikilohydric superpowers is broad and spotty.  The “lower” plants with no roots or veins need it, having no ability to take lift water from the soil and no pipes to move it internally:  some algae, lichens, mosses, and liverworts.     Rootless rain dependence may seem like a drag,   but it is a plus for living rootless on tombstones, telephone wires, and tree trunks.  Some plants with roots and veins, “vascular plants,” have poikilohydric representatives, including fern allies (our local Selaginella),   ferns, and assorted Dicots and Monocots, including a few grasses and sedges.

You might ask, how could so many different unrelated  plants come up with the same bag of tricks?  Well, convergent evolution is not rare, but more tantalizing, the ability of mature plants to go into quasi-death-dormancy is mirrored in something all seed plants have—seeds.  The genetic mechanisms that allow seeds to lie dormant and dry for centuries might extend sometimes in some species into adult life (and death, and life).

spider

Hanging around the liverwort tree, by Donna Rogers

Advertisements
 
9 Comments

Posted by on October 21, 2016 in Uncategorized

 

9 responses to “Zombie Plants – The Green Undead Awaken on Halloween (if it rains)

  1. theshrubqueen

    October 22, 2016 at 8:18 am

    Enlightening! I thought Liverwort was a cold cut.

     
    • George Rogers

      October 22, 2016 at 8:52 am

      No meats in this blog

       
      • theshrubqueen

        October 22, 2016 at 10:59 am

        Wait, it’s Liverwurst or Braunsweiger- not appropriate for vegetarian blog!

         
      • George Rogers

        October 22, 2016 at 7:02 pm

        You know, that sound like a good snack platter.

         
      • theshrubqueen

        October 22, 2016 at 7:52 pm

        I agree – rare to find someone who likes braunswieger (can’t spell it!)

         
  2. Steve

    October 22, 2016 at 8:35 am

    I learned a new word! Poikilohydric, very refreshing (pun intended). Are plants which go dormant in the winter poikilothermic? Or are their responses due mostly to daylight reduction (poikiloluxic?). Have a Happy Halloween everyone. Best horror movie for botanists: The Day of the Triffids

     
    • George Rogers

      October 22, 2016 at 8:54 am

      poi-oh-poi Steve, I’m getting so confused

       
  3. leonorealaniz

    October 22, 2016 at 8:53 am

    Thank you ! Hi Leonore…iy is always such a happy rare treat to hear from you. In honor of the occasion I’m going to make a print todat. Can only dream of how pretty it must be in Western MA eight now.

     
  4. FlowerAlley

    October 22, 2016 at 8:57 am

    Lovely. Several of my favorites here.

     

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

 
%d bloggers like this: