Can someone explain?

[dcarch]

I decided to start a new thread here:

Originally Posted by lightt

There recently was a link posted on GW to a Kansas State University Extension article that explained why it is not only OK, but in many circumstances preferable to pick tomatoes prior to being fully ripe. This is probably more interesting to those who have pest pressures -- especially from pests that wait until the fruit is a just day or so from being fully ripe!
I'm one of those who (at least subconsciously) bought into the grocery store and roadside market "vine ripened" hype although for various reasons I’ve occasionally brought in unripe fruit but didn’t note any taste differences.


I was not aware of a membrane forming that seals the tomato stem -- which pretty much voids the entire concept of "vine ripening"!!

* Inside mature green tomatoes on the vine, two growth-regulating hormones change dramatically, causing the fruit to start producing ethylene gas. The gas makes the fruit cells age – soften, begin to lose their green and develop red, and produce more ethylene .. and so on.

* At the same time, a layer of cells starts to form across a joint in the stem, about one-half inch above the fruit. These cells will seal off the tomato so no additional materials can move into or from the plant.

“By the time the tomato has its first blush of red color, the layer of cells – called an abcision zone – is complete, and you can pick the tomato with no loss of flavor or quality,” Marr said. “If left on the vine after that, all the tomato will do is hang there, disconnected, going through the rest of the ripening process.”

Here's the url for the entire article: http://www.oznet.ksu.edu/news/sty/20...toes071805.htm

Terry Light

1. Has this study/conclusion been confirmed by others?

2. If the almost-ripe fruit is cut off from the plant, then why, as all you have experienced many times, would the fruit split after a heavy rain fall?

3. Has anyone here done a taste test?

Sorry, dumb questions.

dcarch

[WildLife]

Water can still pass through.

[Lee]

Actually, good questions Dcarch!

I would say that if water can still pass through, then there
is no cut off from the main plant that develops.

I can't say I've ever done a good trial of vine ripened vs indoor ripened tomatoes, so I can't comment on that one.

However, I will say an indoor ripened tomato tastes much better than a vine ripened pecked by a bird or munched on by a fruit worm....

Lee

[Linda10]

I've wondered the same thing. Like Lee, I've also have lost too many tomatoes when the birds or insects get to them first. Hope someone knows of reliable studies that confirm this.

[Tormato]

dcarch,

Are you implying that the KS researchers may be insane in the membrane?

Tormato

[dcarch]

Originally Posted by Tormato

dcarch,
Are you implying that the KS researchers may be insane in the membrane? Tormato

If you don't question these studies, then the terrorists have won.

Serious, it's difficult to see how that little piece of membrance can selectively filter out all compounds and chemicals in the fluid and only let water thru to split the fruit, and why would a plant want to do that?

dcarch

[levad]

if anything on my vines starts to ripen im going to try the test. i never have too many pest / bird problems. i will harvest the most ripe before a rain.

if any thing here gets over ripe the little ants get into it for sugar or water or because the skin is softer and they like tomatoes too.

[WildLife]

Reverse osmosis.
Best way to purify water, would not be surprised if
the "membrane" only lets water through.

[dcarch]

Originally Posted by WildLife

Reverse osmosis.
Best way to purify water, would not be surprised if the "membrane" only lets water through.

Good thinking; however:

As I remember, reverse osmosis will require very high pressure, over 300 psi. It's not likely that tomato plants can generate that much pressure.

dcarch

[levad]

300psi i just had a vision of tomatoes blowing apart during a rain shower... sorry...

i do wonder if it is just peculiar to the tomato? no other fruit split this way, do they? i would think berries or melons would suffer the same effects but i dont recall seeing this.

im too limited in knowledge and experience...aka ignorant lol

[lightt]

dcarch,
Here's a link to the thread I referenced on GW: http://forums.gardenweb.com/forums/l...420121779.html

I asked pretty much your exact same question in that thread...

Terry Light

[sic transit gloria]

Edited slightly for public consumption, here's the explanation from the man himself. I went to Kansas State University, so I felt obliged to dig a little deeper...

"Your observations are correct in that tomatoes do frequently crack following a rain when tomato fruit absorb water. Cracking will occur on some varieties that have a non-expandable skin that seems to be variety related although not necessarily thick or thin skins. Some 'thin skinned' tomatoes will not crack while some 'thick skinned' tomatoes crack readily. All plants have 2 types of conducting cells- called xylem and phloem. Water moves from the base of the plant to leaves, fruit, etc through xylem cells. Food reserves (sugars,etc in a water solution) move around the plant in phloem cells- from leaves to fruit, roots, etc. When the layer of cells form to isolate the tomato fruit, this occurs as a plug that develops in the phloem cells. Xylem cells still function to move water into the fruit. However, there is no 'other direction' in the xylem cells. Water can move into the fruit but not out again. This may be a long winded answer to your question but, hopefully, will explain your correct observation in relation to plant anatomy and morphology. Let me know if you have further questions.

Signed,

Chuck Marr"

[TZ-OH6]

Reverse osmosis units work at standard home water pressure (~70 psi?). Many people have them at home under their sinks for purified water. I have a portable one that screws onto the end of the sink faucet or hose bib.

Plain old osmosis is movement of water across a membrane from from an area of low solute concentration to high solutes. Drying soil has a high solute concentration (positive water potential -sorta like a suction force) compared to the plant sap, and can actually pull water from root hairs and kill them. When it rains the water potential reverses as soil water dilutes compared to plant sap, this causes the plant to pull in water, and the resulting "root pressure" increases the hydrostatic pressure in the plant up to a certain height. The height is usually about a meter before the weight of water equals the osmotic force, so I wonder if fruits high up on plants split as much? Sugars, which increase as fruit ripens, affect osmotic potential so there would be another step up in force as the dilute water from the soil/rain enters the plant (diluting the sap). So now you have high pressure sap from root pressure and an increased osmotic force/potential between the fruit and the sap. The fruit is in effect sucking on a fire hose that gets turned on when it rains on dry soil.

[cottonpicker]

As stated above... I also believe it could be "Osmotic pressure".... defined as the hydrostatic pressure produced by a solution on a space, separated from a solvent by a semipermeable membrane, due to a differential in concentrations of solute. Learned this many, many years ago in college and it means that a solution that is less concentrated in dissolved materials will move thru a semi-permeable membrane (abcision cells) toward & into a space of higher concentration of dissolved salts/sugars, etc. OR... from a stem containing low concentration of nutrients thru the abcision cells ( semipermeable) and into the tomato which contains a higher concentration of salts/ sugars, nutrients, etc.

[dcarch]

Hello guys,

I am glad I started this thread.

You are very good.

Very sophisticated reasoning here.

thanks

dcarch